Dynamic background star speed

Background stars now move at increasing pace as player progresses in
game. See Constants.as for the values affecting this.
(Note that the current random expression we use for spawning stars is a
bit strange in that it depends not only on game time, but also on the
rate at which we call updateStarSpawning()... we might want to change
this if we want more uniform star density as the speed of stars
increases)
Merge branch 'master' of https://github.com/quarter-spiral/qs-flash-sample-sdk-integration.git

Conflicts:
	ShootForever/bin-debug/Startup.swf
Music + SFX integration

Added SoundManager for pretty basic music & sound playing. Use
"SoundManager.getInstance().playSound() to... well, you know, play
sounds.
Music track sequencing, auto-loop, etc. not yet added... will add later
if desired.
Current music + sfx are, of course, placeholder... please replace as
needed (and update README.txt license to match)