Reactive Issues Client (Issue #126)

My first pull request - I'm sure there is something I haven't done quite right, but I'm hoping to get some feedback to make future ones better.  I pulled in a couple of other changes so that I could run unit tests and add the Milestones client, but those were already separate pull requests.

Also - I didn't see a pattern for testing observable versions of the clients.  Is there a good example of this somewhere or is it necessary?