DO NOT MERGE: Support for Rackspace Cloud Monitoring

I'm beginning the work to support Cloud Monitoring in pkgcloud. I thought I'd open this PR to keep the work visible, and to get early feedback.

The docs for the Cloud Monitoring API are available at http://docs.rackspace.com/cm/api/v1.0/cm-devguide/content/overview.html

This is still very much a work in progress, so please don't mind extra debugging statements etc.

I definitely plan on including tests, but am still wrapping my mind around how all that works within the project.