Switch license to GPLv3 or later

I've been thinking about this for a while. On the one hand, using the
"or later" clause means we have to place some trust in the Free Software
Foundation. On the other hand, being able to adopt newer versions of the
license without having to contact all contributors is useful for
compatibility (e.g. Apache 2 and GPLv3).

I recently noticed that Section 14 states that new versions of the
license will be "similar in spirit" to the current version. I think this
reduces the amount of trust we need to place in the FSF, as I'd hope
that if a future license did diverge too much from the original spirit
that a court might not consider it valid.

Furthermore, if the FSF went totally crazy, there are many bigger and
more important projects who would experience the same problem.

README.md

@@ -130,22 +130,22 @@ OpenRS2 uses [Semantic Versioning][semver].
 
 ## License
 
-Unless otherwise stated, all code and data is licensed under version 3.0 (and
-only version 3.0) of the [GNU General Public License][gpl]. The full terms are
-available in the `COPYING` file.
+Unless otherwise stated, all code and data is licensed under version 3.0 or
+later of the [GNU General Public License][gpl]. The full terms are available
+in the `COPYING` file.
 
 The `deob-annotations` and `jsobject` modules are instead licensed under
-version 3.0 (and only version 3.0) of the
-[GNU Lesser General Public License][lgpl]. The full terms are available in the
-`COPYING.LESSER` file in each module's directory.
+version 3.0 or later of the [GNU Lesser General Public License][lgpl]. The full
+terms are available in the `COPYING.LESSER` file in each module's directory.
 
 ## Copyright
 
 Copyright (c) 2019-2020 OpenRS2 Authors
 
 OpenRS2 is free software: you can redistribute it and/or modify it under the
-terms of version 3.0 of the GNU General Public License as published by the Free
-Software Foundation.
+terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later
+version.
 
 OpenRS2 is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A

deob-annotations/README.md

@@ -5,8 +5,9 @@
 Copyright (c) 2019 OpenRS2 Authors
 
 OpenRS2 Deobfuscator Annotations is free software: you can redistribute it
-and/or modify it under the terms of version 3.0 of the GNU Lesser General
-Public License as published by the Free Software Foundation.
+and/or modify it under the terms of the GNU Lesser General Public License as
+published by the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
 
 OpenRS2 Deobfuscator Annotations is distributed in the hope that it will be
 useful, but WITHOUT ANY WARRANTY; without even the implied warranty of

deob-annotations/pom.xml

@@ -18,7 +18,7 @@
   </description>
   <licenses>
     <license>
-      <name>GNU Lesser General Public License v3.0</name>
+      <name>GNU Lesser General Public License v3.0 or later</name>
       <url>https://www.gnu.org/licenses/lgpl-3.0.txt</url>
     </license>
   </licenses>

jsobject/README.md

@@ -5,8 +5,9 @@
 Copyright (c) 2020 OpenRS2 Authors
 
 OpenRS2 JavaScript Object is free software: you can redistribute it and/or
-modify it under the terms of version 3.0 of the GNU Lesser General Public
-License as published by the Free Software Foundation.
+modify it under the terms of the GNU Lesser General Public License as published
+by the Free Software Foundation, either version 3 of the License, or (at your
+option) any later version.
 
 OpenRS2 JavaScript Object is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY

jsobject/pom.xml

@@ -15,7 +15,7 @@
   <description>Stubs for the netscape.javascript package.</description>
   <licenses>
     <license>
-      <name>GNU Lesser General Public License v3.0</name>
+      <name>GNU Lesser General Public License v3.0 or later</name>
       <url>https://www.gnu.org/licenses/lgpl-3.0.txt</url>
     </license>
   </licenses>