fix(setup): file() is deprecated. Use open.
feat(tox): add tox support: py27, py33, flake8.

Rationale: make it easy to run test suites against python 3, and also run linting easily.
- tox -e py33 # Python 3 tests
- tox -e flake8 # linting
Merge pull request #34 from cabrera/tox_support

Add tox support