Relicense code changes to MIT and textures changes to CC-BY-SA-3.0

LICENSE.txt

@@ -1,28 +1,45 @@
 Code:
 
-GPLv3, WTFPL (for the changes)
+The mod this is based on was licensed under GPLv3 and can be found in the 0.3
+branch and at https://forum.minetest.net/viewtopic.php?t=658.
+License of my changes:
+SPDX-License-Identifier: MIT
+
 
 
 Textures:
 
-CC-SA, WTFPL (for the changes)
+SPDX-License-Identifier: CC-BY-SA-3.0
+
 
 
 Sounds:
 
-CC by 3.0:
 
+nyanland_cat.*.ogg:
+
+The meow sounds are based on files from freesound.org, from various authors:
+CC by 3.0:
 — http://www.freesound.org/people/dobroide/sounds/95698/
 — http://www.freesound.org/people/Kyster/sounds/79114/
 — http://www.freesound.org/people/Kyster/sounds/82275/
-
-
-Sampling Plus 1.0
-
+Sampling Plus 1.0:
 — http://www.freesound.org/people/oliver%20eye/sounds/56380/
 
+At the time of this writing, the freesound.org website does not work,
+which hinders an association of the sound files in this mod to the above links.
+Listening to the meow sounds and associating them is left as a task for the
+reader. A pull request documenting the result of this task here is welcome.
 
-Unknown License:
 
-— irc(freenode.net)
-— footstep sounds edited from default gravel sounds
+nyanland_portal.*.ogg:
+
+The portal sounds are made from audio captcha generated at freenode.net for IRC.
+Their license is unknown.
+
+
+nyanland_cloud_footstep.*.ogg:
+
+The footstep sounds are edited versions of the gravel sounds in the default of
+minetest_game.
+Their license is unknown.