Changes glm module to use proper buffer API.

This patch changes the glm module to no longer use the hackish method of
support the __getbuffer__/__releasebuffer__ API. It can now be exported
as properly identifying itself as contiguous and rw, if necessary.
Converts the gles2 module to using GLEW.

Instead of using GLES2 directly (which works well in Linux), we now use
GLEW instead. We may remove the gles2 module entirely, later, in favor
of using their own GL module; though this is doubtful.