Move example compositor to subdirectory

TODO

@@ -1,5 +1,17 @@
 Core wayland protocol
 
+ - surface.set_grab_mode(GRAB_OWNER_EVENTS vs GRAB_SURFACE_EVENTS), to
+   make menus work right: click and drag in a menubar grabs the
+   pointer to the menubar (which we need for detecting motion into
+   another menu item), but we need events for the popup menu surface
+   as well.
+
+ - input_device.attach() should use a timestamp so the server can
+   discard late requests (sending a request to set the pointer image
+   in response to a motion event, the pointer leaves and then reenters
+   the surface, before the server receives the reqest -> the server
+   must discard it).
+
  - The message format has to include information about number of fds
    in the message so we can skip a message correctly.  Or we should
    just give up on trying to recover from unknown messages.