WIP on adding tests for the preroller
Improve abort handling in Preroller

* Preroller: Ensure that pump callback is only ever called once
* Preroller: Create our URI once when we get streamKey
* RawAudio: Track our disconnected state
* Shoutcast: Track our disconnected state
* test_preroll_server: Add a tiny server from testing preroller interactions
Merge pull request #22 from StreamMachine/TestPreroller

Improve Abort Handling in Preroller