addon.xml

  - change logic for command/playbackstate:
     - resume/play/1 will now properly resume when pausing, and attempt to
       start play when playback has endeded. Fixes #17
     - pause/2 will now only pause if the player is actually playing.
       It can no longer be used to toggle pause mode.
     - toggle (new) will now toggle pause mode, similarily to how "pause"
       did before

Also updated README.md, which was lagging behind describing new settings