add several values for following commits
change _fitText to _update

I realized it makes more sense to call the function responsible for
fitting the border and background around the text _update and call it
asynchronously. I've also simplified the process to put space between
multiple lines by adding a _font.spacing attribute. Finally, _dis.context
now permanently tracks it's font attribute so that the proper line width
can be calculated in the _update function.
unbind _update as it is redundant
add start and stop functionality

In order to properly start and stop the engine, the user should activate
an event. In this case I've simply added an onclick method to the canvas.
The first time it is clicked, all sounds will silently play for 50
milliseconds to preload them (a hack to get around apple's safari policy).
Also all sprite _update functions and sound play functions
will start and stop with the engine. This brings the whole engine
together and is much more natural than the old setup.
make TextBox update and draw correctly

I have finally found the correct combination for drawing the
TextBox class regardless of font size, text alignment, border or
margins. There should be no more problems with it.