Documentation: Please clarify music licenses.

[0lhi]

At https://github.com/SuperTux/supertux/blob/master/data/AUTHORS , the following things remain unclear:

• [ ] Does "CC-BY-SA" refer to CC-BY-SA 1.0 specifically, or any version of the license? Does it vary per soundfile?
• [ ] How are ZhayTee's files licensed?
• [ ] Does "GPL" refer to GPLv1, or any version of the license?
• [ ] How are christmas_theme.ogg and classic.ogg licensed?
• [ ] Is the included version of salcon.ogg the free one?

I'd appreciate if you could add the information to the authors file, and a link to every license mentioned.

[Mathnerd314]

I think CC by SA is mainly 2.0 for all files. 2.0 was released in 2004 which was around the time licensing was an issue. https://discarded-ideas.org/ seems to have updated to CC-BY-SA 4.0.

According to Discord, "supertux ice level music is the same as ZhayTee - 4096 from his album 4096." Given the lack of license information (retro is really old music) I would assume it is also CC-BY-SA 2.0

GPL refers to "GPL version 2 or later"

christmas_theme was added by @tobbi, ask him: https://github.com/SuperTux/data/commit/ee2116d44444f2f314ef00276bcd38cbadc01864

No idea about classic

salcon was remixed to remove an unfree sample, it should be free

[tobbi]

Christmas theme by Krobonil under the same license that intro theme is under: https://forum.freegamedev.net/viewtopic.php?f=67&t=6587