Description of OpenGL ABI for AROS

1. Library

Library shall be named gl.library. The initial version of the library is 20.
The library base variable shall be called GLBase.

2. Vector table

Library exposes OpenGL 1.3 + ARB_multitexture extension in its vector table.
Native API (glA) is exposed in first 30 free LVOs. The exact placement of each
function can be referenced in the included gl.conf.

All exposed library functions shall use stack call calling convention.

3. Library base

Implementation should assume that the library base WILL NOT be passed to the
library functions during the call. This is due to a fact that extension
functions retrieved via glAGetProcAddress will not follow the standard AROS
shared library function calling ABI. They will be called via function pointer
according to C calling convention.
