command: add video-rotate property
command: add playback-abort property

Now this is obscure.
command: add cursor-autohide property

Allows properly changing/updating the cursor state. Useful for client
API window embedding, because the host application may not want the mpv
window to grab mouse input, and this has to manually handle the cursor.
Changing the cursor of foreign windows is usually not sane.

It might make sense to allow changing the cursor icon, but that would be
much more complicated, so I won't add it unless someone actually
requests it.
lua: don't use "output" as identifier

I suspect this clashes with libcs,w hich define "stdout" as macro.
Hopefully fixes #1206.