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!

- Renamed VERSION to RAYLIB_VERSION
- Renamed API_VERSION to RAYLIB_API_VERSION
- Renamed RAYLIB_RELEASE to RAYLIB_RELEASE_PATH
- Support Web Assembly compilation on PLATFORM_WEB

OpenAL Soft backend is still available in audio module, I'm thinking if
exposing it for building in some way or just left it there for advance
users to switch to it manually in case of necessity...

It seems there are some platform-dependant issues

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

I've added .PHONY targets and fixed "clean" recipe.

I've renamed all makefile files to "Makefile" because they appear in the first files.

I've added "-ldl" library, it's necessary to compile the project.

I've cleaned the GNU/Linux compilation, now you can compile without useless parameters.

If you have raylib on standard directories ("/usr/local/include/raylib/raylib.h" for the header and "/usr/local/lib/libraylib.a" for raylib library) you can compile without edit the makefile.

I've changed all default target names with 'all'. Here there is the explanation: <https://www.gnu.org/prep/standards/standards.html#Standard-Targets>.

Now support multiple platforms

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