Document wl_proxy user data surprises
Submitted by Pekka Paalanen
Assigned to Wayland bug list
People get surprised, that for a wl_proxy:
- add_listener can only be used once, so it's more a "init", not "add"
- add_listener sets the same user data as set_user_data does
Might as well review that all aspect of the user data are documented.
This should be both in the per-function doc comments picked up by Doxygen, and when a "big docs" chapter about the client side API gets started, there.