Mingw fixes (Azimer#13)

* Makefile: simplify & fix
* AziAudio: fix mingw
* Makefile: add missing c target and correct cpp target
* Makefile: slightly simplify it more
* AziAudio: warning fixes for mingw
* Makefile: add WASAPISoundDriver
* AziAudio: fix mingw compilation
* Makefile: add missing lib to LDFLAGS