A new event handling API

Instead of many callback functions, use a single event callback function
that takes a struct with an enum and a union.
glwtWindowSetTitle
Fix duplicate keysym

GLWT_KEY_COMMA and GLWT_KEY_MINUS had equal values. Fix'd!
Raspberry Pi OpenGL ES support

Raspberry Pi OpenGL ES initialization using the proprietary Broadcom
firmware libraries.
Implemented the OSX port.
X11: Silently ignore events for destroyed windows

After a window has been destroyed and the corresponding entry in X11
Context has been removed, there may still be events in the X11 event
queue for that window remaining.

Silently ignore any events for windows which are not found in the X11
context using XFindContext.
Converted the OSX port to C89

It now builds with llvm-gcc-4.2 shipped by apple.
Also fixed some warnings
X11: Avoid C99 struct initializers