Specify Python version in .travis.yml

Fix bug when creating temporary URLs

Pythons HMAC does not accept unicode, therefore converting key and hmac body to
string (to be compatible with Python 2.x). Python 3 needs a byte conversion.

See also: http://bugs.python.org/issue5285

Include bugfix for recent Django versions

Minor fixes in setup.py / MANIFEST.in, version bump to 0.2

Add Django >= 1.5 requirement