Implement surface_attach method. This is called when a client attaches an shm
buffer with wl_surface_attach().
Implement the GLES2 interface for attaching shm buffers. This creates an opengl
texture with the shm buffer contents for the surface.
This commit also includes some working code to render the surfaces onto the
screen for demonstration purposes.
Add the wayland surface interface to the example compositor.
Implement the create_surface method to create a new wlr surface from the
wayland surface and add the interface.
