Pencil mode

The user can now put more than one number in a cell as a reminder. The
method I am using to calculate the font size is kind of hacky. If I
have time, I may consider using a plugin such as jQuery Inputfit to do
it more precisely.
Minor visual changes to numbers

They should be a little easier to read.
Visual change to pencil mode

Cells turn gray if they have more than one digit in them.
Tweaked code to access rows, columns, and boxes

It is slightly simpler.