Moving event handlers to Board.js

For issue #8.

Wrapped methods in Driver.js inside a self-executing anonymous function
to keep them from polluting the global namespace. I'm generally trying
to give the impression that this file is a static program runner, which
is sort of is.

Wrote event handler methods in Board.js which handle arrow keypresses.
Loaded this into the browser to verify that arrow presses register
correctly.

Wrote comments (not really pseudocode...) describing what the method
should do. It's just a high-level look for right now and I already see
some stuff that will probably need to be tweaked but the comments should
serve for a decent baseline in the meantime.