New: added override instruction for TabMixPlus XBL proxy file
Change: the tabmixplus binding proxy is overridden with binding from this
addon.

The bug566510 compatibility binding moved from tabmixplus addon here.
Change: compatibility binding for tabmixplus renamed.
Change: tabmixplus's XBL proxy moved to different folder.
New: added compatibility.js to handle some hacks for other addons;
TabMixPlus hacks included here
Merge branch 'issues/1-proxy'. Fixes #1.