Attempt 2 to learn Unicode (uniobjs)

[Nicolas Sebrecht]

I call this branch "uniobjs". It introduce the "uni" module with objects
handling the encodings, instead of working with functions like before. 

Again, I don't expect a full review. It's large and quiet boring sometime. The
more intersting parts are the patches 1/4 and 3/4.

The uni-tests.py might worth a run.

The diffs online: https://github.com/nicolas33/offlineimap/compare/OfflineIMAP:next...ns/uniobjs?expand=1
The branch TIP: https://github.com/nicolas33/offlineimap/commits/ns/uniobjs

The more important files you should focus on:

API: https://github.com/nicolas33/offlineimap/blob/ns/uniobjs/docs/doc-src/API.rst#id23
uni: https://github.com/nicolas33/offlineimap/blob/ns/uniobjs/offlineimap/utils/uni.py


[PATCH 1/4] docs: API: introduce unicode module
[PATCH 2/4] add IMAPClient embedded module to work with IMAP UTF-7
[PATCH 3/4] introduce utils/uni.py module
[PATCH 4/4] learn unicode support