Ensure "progress" fires with 100%

In the event that progress does NOT fire with loaded==total, then fire it with 100% when the load event happens
Initialize lastPause during load()

Typo had load() setting lastPlay twice instead of lastPlay and lastPause once each
Fire "finish" event ONCE when audio ends 

Properly check for end of playback with valid buffer available for getDuration(), and ensure "finish" only fires once per play
Merge pull request #225 from rgagnon24/master

Re-add working 'finish' event, fix missing initialization, ensure 100% loading event