Bug 1078520 - python client

Implement a python client.  Note to reviewers, there were a couple fairly substantial changes to the way the module in the latest commits.  It's probably best to only really look at the most recent code.
I think my long term plan is to have every component upload it's docs to references.taskcluster.net, not just references; but also markdown, images, etc... 

Then we can make a docs generator to generate docs.taskcluster.net from references.taskcluster.net... And the docs generate can probably make the URLs to the references more visible in the documentation.

Either way, this is something people don't care about... The current hack is fine. And certainly fine for now..