CircleCI Continuous Integration

This pull request will add support for the CircleCI continuous integration platform, which will configure all the necessary environments (PostgreSQL 9.0 -> 9.4 beta, Python 2.5 -> 3.4 excl 3.0 & 3.1, PyPy, Jython) and run the tox configuration to run all unit tests across the configured platforms.

Work-in-progress: The configuration is almost complete, just testing the Python 2.5 and Jython environments with the run_25 command, then maybe adding a badge to the README file.