Added missing OpenGL 2.0 and 2.1 functions to wrapper (#28)

* Added missing OpenGL 2.0 and 2.1 functions to wrapper

other notable changes:
* enum parameter used by `blendEquationSeparate` is now also used by `blendEquation` in OpenGL 1.4,
* extracted enum parameter used by `getProgramiv` to its own type,
* adjusted `uniformMatrix4fv` to be consistent with other functions like it.

* Added missing assert in `validateProgram`

Author: hazeycode