added howler.js to libs and readme
finally fixed rotated turret logic

there was a really really big bug in the turret logic code from the
start that I never noticed because the turrets I tested with were at a
90 degree angle. the bug arose from easeljs rotations essentially
reading 0 as -90 when converted to degrees, which I never noticed due to
my 90 degree rotated turrets cancelling it out and making the systems
appear equal. took forever to fix, really glad to have it out of the way