Review raylib_icon resource

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

Note that only some lib versions have been updated

Not required any more!

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...

To be more generic and configurable

mingw32 libraries provided were compiled with a different GCC version
(different computer) and seemed to be incompatible on linkage (missing
symbols).