Image: Rename save to save_bmp

* The save method variant with the second argument is also removed
(no point in keeping it around)
BUGS.md: Remove file (redundant)

* GitHub Issues tracker is preferred
Fix several compile warnings with type conversion

* MSVCPP complained about potential data loss with mixing 32-bit/64-bit
values
Fix OpenAL AL_INVALID_OPERATION err
examples/audio: Clean up source a bit