Add Python 3 support.

Closes #43 #50.
Complete Python 3 support.

- Reorganize some imports
- Fix encoding name: s/utf8/utf-8/
- Add trove classifiers for Python 3.2, 3.3 and 3.4
- Bump version to 0.6.
Update .travis.yml.

Run tests against Python 3.2 and 3.3.
Upgrade paramiko to 1.13.0.
Update version info in Sphinx.