Feature/api version support (#109)

Set of changes that adds basic Facade Version support.

Instead of building a monolithic _client.py, we build a _client<version>.py for each integer Facade version, and put Facades there.

One issue is that we store the auxillary classes in a single, monolithic _definitions.py. We should probably refactor to split those up by Facade version. For now, they all seem to be backwards compatible, and all tests pass.

(I've tested against 2.0.2, 2.1.2, 2.2-alpha1 and 2.2-beta2.)

Also ninja'd in a call to the Pinger class, which should prevent timeouts in JaaS.