Fixes resize issue (again)

The init() function created a new <canvas> element each time it ran,
which meant trying to stuff multiple <canvas>es into a single div every
time the resize() function was called (which itself calls init()); now,
the resize() function .remove()s the initial <canvas> before init()
creates it again.
Merge branch 'master' of https://github.com/bigsweater/jQuery-Canvas-Starfield