Full Sublime Text 3 compatibility.

I've been trying to port some of my favorite Sublime Text 2 plugins to Sublime Text 3.

I believe I've tested all functionality and have everything working in ST2. However, it isn't backwards compatible with ST2.

I'll let you decide how you want to handle compatibility. I see that you were making some initial attempt at importing from __future__ to attempt to keep it compatible. I plan on keeping this in a python3 branch for now, and certainly wouldn't mind if you did the same.

Thanks for the plugin!