A few protocol additions: wl_surface.offset allows clients to update
a surface's buffer offset independently from the buffer,
wl_output.name and description allow clients to identify outputs
without depending on xdg-output-unstable-v1.
In protocol definitions, events have a new "type" attribute and can
now be marked as destructors.
A number of bug fixes, including a race condition when destroying
proxies in multi-threaded clients.