Function gl::CopyTexSubImage2D

pub unsafe fn CopyTexSubImage2D(target: GLenum,
                                level: GLint,
                                xoffset: GLint,
                                yoffset: GLint,
                                x: GLint,
                                y: GLint,
                                width: GLsizei,
                                height: GLsizei)

Fallbacks: CopyTexSubImage2DEXT