[sugar] Python Style Guide

[Marco Pesenti Gritti]

Ian Bicking wrote:
> I've applied the changes we have so far.
>
> Generally, I think we should try to get diff-busting changes in early, 
> like switching to spaces from tabs.  Other changes don't seem as 
> urgent, especially if they can cause regressions; but I'm not entirely 
> clear on timelines, so I'll defer to you guys.  Most important seem to 
> be the set of changes which are easy and mostly safe, but mess up 
> history.

Agreed, let's do most invasive changes asap...

Marco