Sxiv python wrapper.

I wrote a small python wrapper.

I haven't much time for now as I'm very involved in a load of other projects. But I really wanted to get it fixed, so here is my quick and dirty workaround, since I'm not very proficient with python.

This is a standalone wrapper for sxiv, it does not make use of the ranger API. Sorry if I haven't studied the plugin API, but I lack the time. Works for python 2.7 and 3.3. I guess we could do some additional optimizations with ranger, like passing the file list directly which would reduce the load time.

Performances are correct, but not that great. A bit better than the shell wrapper I would say. For me that's  approx. 2 seconds for 2000 pics. 

In ranger 1.5.5 apps.py could fetch values directly from the ranger API (the 'c' parameter!). But in the default rifle.conf there is absolutely no python code. I'm wondering if that means we cannot exec python code anymore.