Seems like this confused users quite often.
Instead of --profile=pseudo-gui, --player-operation-mode=pseudo-gui now
has to be used to invoke pseudo GUI mode. The old way still works, and
still behaves in the old way.
And split the Cocoa and Unix cases. Simplify the Cocoa case slightly by
calling mpv_main directly, instead of passing a function pointer. Also
add a comment explaining why Cocoa needs a special case at all.
