Context initialization should properly check required GL version

[einarf]

settings:

OPENGL = {
    "version": (3, 3),
}

Should be translated into version code 330 and passed into:

• moderngl.create_context(version_code=version)
• moderngl.create_standalone_context(version_code=version)

This way we will actually see an error message that makes sense when the GL version required is not met.

[einarf]

ddf10c3e074d8802b259909d527ed3b18ac46be9