Collider Engine Licensing & library split-off

[BenjamenMeyer]

Vega Strike is primarily a GPL-licensed program. However, there have been several libraries integrated into the code that we now need to validate the licensing for and ensure we tag the files with the correct licensing:

• engine/src/cmd/collider2 is generally code taken from OPCODE 1.3 available at http://www.codercorner.com/Opcode.htm which is under something akin to a public domain license - per the website: You’re free to use them in any commercial or non-commercial program. However no license is provided with the code itself, just a basic copyright and description. We should assume that the base code is public domain; per https://www.gnu.org/licenses/gpl-faq.en.html we should be able to dual license the files - essentially, the original is marked public domain and then our modifications are GPL. There's also a couple text files that seem to be missing from the original zip file; we should include them as part of making this its own internal library.
• engine/src/cmd/collider2 contains some code related to Crystal Space 3D. We need to investigate this as the current code in GitHub looks like its LGPL licensed. Was that always the case? If not, can we find the version that was GPL licensed? Or do we need to change the license on those files to LGPL?
• for 0.10.x (master) we'll move it to its own library as part of the build system which will make it easier to manage long term

Both of these are about getting the license correct so we can do tasks like #991 and get it right. This shouldn't prohibit us from making some standard templates for all of the files - rather this should encourage us to do so.

For 0.9.x we should do the minimum we need to; let's just make sure we get the licensing right and may be standardize it as well.
For 0.10.x (current master as of 2025-01-20) we can do more.

[BenjamenMeyer]

CrystalSpace:

• https://sourceforge.net/projects/crystal/
• someone forked it to GitHub; SF seems to have had a little more life than GitHub but overall looks unmaintained

[BenjamenMeyer]

Based on http://www.codercorner.com/OpcodeUsers.htm it looks like OPCODE came to us through CS.