Run tests is travis

- Run tests in travis under python2.7 and python3.4
- Add build status badge to README.
Add support for python 3

The unicode function is not in python 3 as string literals are by
default unicode strings.

see:
http://www.diveintopython3.net/porting-code-to-python-3-with-2to3.html#unicode
Merge pull request #4 from robyoung/py3k

Add Python 3 support