Merge pull request #307 from trinketapp/turtle-suspensions

Beginnings of turtle via suspensions
Merge pull request #308 from trinketapp/turtle-suspensions

Updated anonymous turtle methods to use suspensions
Merge branch 'master' into turtledev
Merge branch 'turtle-suspensions' of https://github.com/trinketapp/skulpt into trinketapp-turtle-suspensions
Merge branch 'trinketapp-turtle-suspensions' into turtledev
Cleans up/fixes heading calculations

better/simpler angle calculations
better $circle logic
fixes errors with setx, setx and write
Adds event handling capability to turtle

adds a MouseManager and EventManager class for tracking events
adds onclick onrelease and ondrag to turtle
adds onclick onscreenclick and ontimer to screen
update bgcolor to color the screen canvas and not the canvas container