forked from: Transition Sketcher

author Jesse Freeman aka @theFlashBum | http://jessefreeman.com

This is the Doc Class to run my SketchArea. This class adds keyboard support
to help control features of the SketchArea. Here is a list of all the keys
I have set up.

Keyboard Short Cuts

Space Bar - flips between src a and src b. Source A is always the bottom
layer and Source B is the paint layer.

r - Redraw last animation.

c - Clear SketchArea

s - Quick save. The SketchArea will take the last set of recorded points
along with what mode it is in and save it to a number key. For example if
nothing has been saved and you hit save it will register at key 1. Next
save will be key 2, etc.

1 - 0 Plays back a saved animation.

d - Activates the draw tool. Once in draw mode you will see a representation
of the brush that follows the mouse. When you are done you can hit d to
exit draw mode. Hitting replay automatically exits you from draw mode.

+ - Increases the size of the brush.

- - Decreases the size of the brush.

The 