Doc: use a markdown version of GPL v2 for COPYING.md, also restore a missing line about copying to the GPL v2 wording

COPYING.md

@@ -1,16 +1,17 @@
 This is the license which applies to OpenTTD with the exception of some
-3rd party modules. See README.md for details
+3rd party modules. See [./README.md](./README.md) for details
 
+GNU General Public License
+==========================
 
-                    GNU GENERAL PUBLIC LICENSE
+_Version 2, June 1991_
-                       Version 2, June 1991
+_Copyright © 1989, 1991 Free Software Foundation, Inc.,_
+_51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA_
 
- Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
- 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.
 
-                            Preamble
+### Preamble
 
 The licenses for most software are designed to take away your
 freedom to share and change it.  By contrast, the GNU General Public
@@ -40,8 +41,8 @@ you have.  You must make sure that they, too, receive or can get the
 source code.  And you must show them these terms so they know their
 rights.
 
-  We protect your rights with two steps: (1) copyright the software, and
+We protect your rights with two steps: **(1)** copyright the software, and
-(2) offer you this license which gives you legal permission to copy,
+**(2)** offer you this license which gives you legal permission to copy,
 distribute and/or modify the software.
 
 Also, for each author's protection and ours, we want to make certain
@@ -60,10 +61,9 @@ patent must be licensed for everyone's free use or not licensed at all.
 The precise terms and conditions for copying, distribution and
 modification follow.
 
-                    GNU GENERAL PUBLIC LICENSE
+### TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
-   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
 
-  0. This License applies to any program or other work which contains
+**0.** This License applies to any program or other work which contains
 a notice placed by the copyright holder saying it may be distributed
 under the terms of this General Public License.  The "Program", below,
 refers to any such program or work, and a "work based on the Program"
@@ -80,7 +80,7 @@ is covered only if its contents constitute a work based on the
 Program (independent of having been made by running the Program).
 Whether that is true depends on what the Program does.
 
-  1. You may copy and distribute verbatim copies of the Program's
+**1.** You may copy and distribute verbatim copies of the Program's
 source code as you receive it, in any medium, provided that you
 conspicuously and appropriately publish on each copy an appropriate
 copyright notice and disclaimer of warranty; keep intact all the
@@ -91,20 +91,18 @@ along with the Program.
 You may charge a fee for the physical act of transferring a copy, and
 you may at your option offer warranty protection in exchange for a fee.
 
-  2. You may modify your copy or copies of the Program or any portion
+**2.** You may modify your copy or copies of the Program or any portion
 of it, thus forming a work based on the Program, and copy and
 distribute such modifications or work under the terms of Section 1
 above, provided that you also meet all of these conditions:
 
-    a) You must cause the modified files to carry prominent notices
+* **a)** You must cause the modified files to carry prominent notices
 stating that you changed the files and the date of any change.
-
+* **b)** You must cause any work that you distribute or publish, that in
-    b) You must cause any work that you distribute or publish, that in
 whole or in part contains or is derived from the Program or any
 part thereof, to be licensed as a whole at no charge to all third
 parties under the terms of this License.
-
+* **c)** If the modified program normally reads commands interactively
-    c) If the modified program normally reads commands interactively
 when run, you must cause it, when started running for such
 interactive use in the most ordinary way, to print or display an
 announcement including an appropriate copyright notice and a
@@ -135,22 +133,20 @@ with the Program (or with a work based on the Program) on a volume of
 a storage or distribution medium does not bring the other work under
 the scope of this License.
 
-  3. You may copy and distribute the Program (or a work based on it,
+**3.** You may copy and distribute the Program (or a work based on it,
 under Section 2) in object code or executable form under the terms of
 Sections 1 and 2 above provided that you also do one of the following:
 
-    a) Accompany it with the complete corresponding machine-readable
+* **a)** Accompany it with the complete corresponding machine-readable
 source code, which must be distributed under the terms of Sections
 1 and 2 above on a medium customarily used for software interchange; or,
-
+* **b)** Accompany it with a written offer, valid for at least three
-    b) Accompany it with a written offer, valid for at least three
 years, to give any third party, for a charge no more than your
 cost of physically performing source distribution, a complete
 machine-readable copy of the corresponding source code, to be
 distributed under the terms of Sections 1 and 2 above on a medium
 customarily used for software interchange; or,
-
+* **c)** Accompany it with the information you received as to the offer
-    c) Accompany it with the information you received as to the offer
 to distribute corresponding source code.  (This alternative is
 allowed only for noncommercial distribution and only if you
 received the program in object code or executable form with such
@@ -173,7 +169,7 @@ access to copy the source code from the same place counts as
 distribution of the source code, even though third parties are not
 compelled to copy the source along with the object code.
 
-  4. You may not copy, modify, sublicense, or distribute the Program
+**4.** You may not copy, modify, sublicense, or distribute the Program
 except as expressly provided under this License.  Any attempt
 otherwise to copy, modify, sublicense or distribute the Program is
 void, and will automatically terminate your rights under this License.
@@ -181,7 +177,7 @@ However, parties who have received copies, or rights, from you under
 this License will not have their licenses terminated so long as such
 parties remain in full compliance.
 
-  5. You are not required to accept this License, since you have not
+**5.** You are not required to accept this License, since you have not
 signed it.  However, nothing else grants you permission to modify or
 distribute the Program or its derivative works.  These actions are
 prohibited by law if you do not accept this License.  Therefore, by
@@ -190,7 +186,7 @@ Program), you indicate your acceptance of this License to do so, and
 all its terms and conditions for copying, distributing or modifying
 the Program or works based on it.
 
-  6. Each time you redistribute the Program (or any work based on the
+**6.** Each time you redistribute the Program (or any work based on the
 Program), the recipient automatically receives a license from the
 original licensor to copy, distribute or modify the Program subject to
 these terms and conditions.  You may not impose any further
@@ -198,7 +194,7 @@ restrictions on the recipients' exercise of the rights granted herein.
 You are not responsible for enforcing compliance by third parties to
 this License.
 
-  7. If, as a consequence of a court judgment or allegation of patent
+**7.** If, as a consequence of a court judgment or allegation of patent
 infringement or for any other reason (not limited to patent issues),
 conditions are imposed on you (whether by court order, agreement or
 otherwise) that contradict the conditions of this License, they do not
@@ -230,7 +226,7 @@ impose that choice.
 This section is intended to make thoroughly clear what is believed to
 be a consequence of the rest of this License.
 
-  8. If the distribution and/or use of the Program is restricted in
+**8.** If the distribution and/or use of the Program is restricted in
 certain countries either by patents or by copyrighted interfaces, the
 original copyright holder who places the Program under this License
 may add an explicit geographical distribution limitation excluding
@@ -238,7 +234,7 @@ those countries, so that distribution is permitted only in or among
 countries not thus excluded.  In such case, this License incorporates
 the limitation as if written in the body of this License.
 
-  9. The Free Software Foundation may publish revised and/or new versions
+**9.** The Free Software Foundation may publish revised and/or new versions
 of the General Public License from time to time.  Such new versions will
 be similar in spirit to the present version, but may differ in detail to
 address new problems or concerns.
@@ -251,7 +247,7 @@ Software Foundation.  If the Program does not specify a version number of
 this License, you may choose any version ever published by the Free Software
 Foundation.
 
-  10. If you wish to incorporate parts of the Program into other free
+**10.** If you wish to incorporate parts of the Program into other free
 programs whose distribution conditions are different, write to the author
 to ask for permission.  For software which is copyrighted by the Free
 Software Foundation, write to the Free Software Foundation; we sometimes
@@ -259,9 +255,9 @@ make exceptions for this.  Our decision will be guided by the two goals
 of preserving the free status of all derivatives of our free software and
 of promoting the sharing and reuse of software generally.
 
-                            NO WARRANTY
+### NO WARRANTY
 
-  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+**11.** BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
 FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
 OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
 PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
@@ -271,7 +267,7 @@ TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
 PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
 REPAIR OR CORRECTION.
 
-  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+**12.** IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
 REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
 INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
@@ -283,7 +279,7 @@ POSSIBILITY OF SUCH DAMAGES.
 
 END OF TERMS AND CONDITIONS
 
-            How to Apply These Terms to Your New Programs
+### How to Apply These Terms to Your New Programs
 
 If you develop a new program, and you want it to be of the greatest
 possible use to the public, the best way to achieve this is to make it
@@ -321,9 +317,9 @@ when it starts in an interactive mode:
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.
 
-The hypothetical commands `show w' and `show c' should show the appropriate
+The hypothetical commands `show w` and `show c` should show the appropriate
 parts of the General Public License.  Of course, the commands you use may
-be called something other than `show w' and `show c'; they could even be
+be called something other than `show w` and `show c`; they could even be
 mouse-clicks or menu items--whatever suits your program.
 
 You should also get your employer (if you work as a programmer) or your