Add license for libretro portions

[inactive123]

As per earlier discussion, this time without the ToadKing parts.

[inactive123]

I'd like to at least see this on the libretro files. You might feel fucked over by certain guys that are taking advantage of your work, and that's understandable, I can sense where this is coming from. Well, consider that the same way you feel is how I feel when it comes to the libretro port. I at least want it to be made perfectly clear that I am a copyright holder on the libretro port, and that will then ensure that nobody will ever be making money off this port since I won't ever give my consent away. Right now there are no guarantees or safeguards in place to prevent that. I am upholding both the letter and the spirit of the license in this case.

What you guys do with another port or whatever is your 'business' in case you do anything behind closed doors, but as far as libretro is concerned, nobody will be making any money off it. Not now, not ever.

EDIT: This is how the snes9x team helped me at least when dealing with this issue - snes9xgit/snes9x#133

We can make a firm stand here that will deter any would-be infringers again in the future, together with talks we are having with Raspberry Pi to add things like Recalbox and Lakka to their 'noobs' section so that it will be easy as dirt to install on a Pi, that will directly render kickstarted boxes like this useless in the future, along with their middlemen.

[ekeeke]

That's fine and should be enough to prevent commercial use of libretro core without your consent but why all files have "Genesis Plus GX configuration file support" in their header? It seems like its was copied from config.c and should be updated to reflect each file purpose.