Use tox to launch tests

This allows to test different versions of Python in one go.
Configure the repository to use Travis CI

This doesn't test Python 2.6, since I don't know how to install unittest2
only if we are testing this version of Python.
Update the README for the new test infrastructure
Merge pull request #18 from multani/test-ci

Improve test infrastructure
add gitignore
tox.ini: add python 3.3
README.dm add test instruction
README.md: Add travis-ci badget.
Add version number to module

fix #19