Updated .gitignore file

Source: https://github.com/github/gitignore/blob/master/Python.gitignore
tox: Added basic tox.ini configuration
tox: Test with different SQLAlchemy versions (0.8.4 and 0.9.2)
TravisCI: Use tox for test running
Merge pull request #74 from Turbo87/tox

Tox support