Add Bus and BufferedEventSource
Convert progress event types to strings in JSON
Fix inconsistencies between net45 and net40
Change version to 0.5.4
Beta 0.5.4 (Bus, BufferedEventSource)

Summary merge: 'beta-fixes'

* Change version to 0.5.4
* Fix inconsistencies between net45 and net40
* Convert progress event types to strings in JSON
* Add Bus and BufferedEventSource