Same functionality could be achieved using FLAGS... but also considering removing raylib logo animation...

- Preparing MP3 files support
- Jumped version to raylib 2.0-dev (too many breaking changes...)

Inspired by #504.
Instead of requiring the user to do PLATFORM_ANDROID #ifdefery,
have the android_main entry point exported by raylib and call
the user-defined main. This way many games could (in theory)
run unmodified on Android and elsewhere.

This is untested!