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!

Game developed in the GGJ18, it has some bugs and ending screen is
incomplete... I'll try to keep working a bit more on it.

- Removed useless templates
- Reviewed all Makefiles
- Rework some code for Android support
- Added resources to advance template

Some basic to advance templates are provided to be use as base code for
new games