document new functions. link to new example from audio page, index, and index-offline.
AudioManager: isPaused(name); isPlaying(name). play options: time, duration. soundsheet explanation. minor wording fixes.
note that some things only work for background sounds: isPlaying; setTime; getTime; play with time in opts.
getDuration
Merge pull request #187 from gameclosure/feature-audio-time

document new functions. link to new example from audio page, index, and ...