This commit should bring the mini_al backend up to feature parity with
the OpenAL backend.

To be more generic and configurable

Variable t was read and modified without interleaving sequence points,
technically undefined behavior. Report by Clang's -Wunsequenced

It should be reviewed more carefully...

Requires some work, distortion shader could be move out of raylib to
example code...

Added: DrawRectangleGradientV()
Added: DrawRectangleGradientH()

Increment raylib version and so lib version number.