change translate tween to overriding technique
change translate-to-path tween to overriding technique
scale tween
xscale tween
rotate tween
rotate-to-path tween + few minor tests
alpha tween, the last one
Merge pull request #63 from Animatron/tests

Same-type tweens are now overwrite each other
Merge pull request #64 from Nek/spritesheets

Spritesheets