Better Python backend

[jorgenschaefer]

RopeMacs, Pymacs, etc. is quite heavy, especially as I (personally) mainly use it to get possible completions. We could see if we can rewrite that part.

• Define an RPC protocol between Python and Emacs we can use. Probably JSON-based.
• Use available completion helpers (from rope, jedi, rlcompleter, own stuff?)

How to use Rope as a library:

http://rope.sourceforge.net/library.html

Especially the codehelper part is relevant.