246 custom start time offset support

This patch offers you to have a custom start time for a video.
See issue 246 for more details: https://github.com/zencoder/video-js/issues/246

Description:
By setting the value "starttime" in the data-setup array, any user can specify a custom start position for a video. Playback will start from that given offset.

Requirements:
Preload attribute in html5 video tag MUST be set to auto

Usage:
For example: {'start-time':80} 
This would start video playback from 00:01:20 -> HH:MM:SS
Not setting start-time will start playback from 0 like normal.

Compatibility:
Works with the latest build of VideoJS.

-Joseph Afework