remove all non-pstats formats and change graph format to include milliseconds. add py.test and tox for running test.

[mjbryant]

Pretty large change. Mostly deleting non-pstats stuff. The only substantive changes are:

1. Better (i.e. actually runnable) tests
2. Including milliseconds in graph nodes
3. General cleanup in the main function to make future changes a bit easier.

[ArnaudBrousseau]

Add a comment with a reference to the original project here? Something like "this is a fork of [link to original] tailored to Yelp's need.

[ArnaudBrousseau]

Looking good otherwise, that's a lot less code to maintain! We can add support for whatever format we need afterwards, for now, pstats is all we need.