- added optional startTime parameter to Crafty.audio.play() function for specifying the start position of playback in seconds (defaults to zero)
- a bunch of changes to car sounds
    - changed car idle sound to a better sound IMHO, which constantly loops
    - introduced accelerating and slowing down sounds
    - introduced a top speed sound which begins to play in a loop once acceleration has occurred for 1.5 secs
Note: for looping sounds I attempted to fix the non-seamless loop problem (ie. gap in play) by increasing the sound length and also fading in/out