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!
Supported UTF8 range equivalent to [128..255] (80h..FFh)
Exposed and renamed text function GetGlyphIndex()
Renamed spriteFont parameter name to simply font
Small security check on transmission mission ending screen
