Python 3 support

Tested with:
- Python 3.3 / Django 1.6
- Python 2.7 / Django 1.6
- Python 2.7 / Django 1.3
Simple back: use chunks iterator

This is more appropriate than the default line-based iterator. Also
the default iterator is broken in Python 3 / Django 1.6 (Django bug
22107) which results in abysmal slowness with large files.
Fix imports
Fix PEP 8
Add missing import from future
Merge pull request #1 from davidfischer-ch/master

Fix imports and PEP 8
Fix serving files with unicode filename (e.g. "Pépé à la plage.jpg")

Closes #2.
Merge branch 'pdewacht-master'
Version 0.3.6