[HOpenGL] GLSL interface

[Daniel Bergey]

What is the recommended way to create and use a Shader object?
Graphics.Rendering.OpenGL.GL.Shaders.Shaders has a function createShader
which looks good, but is not exported.  Similar not-exported functions
seem to exist for the Program type.

If there's still work do be done on this part of the library, I can
to test out some code and submit a pull request.

Thanks,
bergey