Tabs seem to break box-drawing in print mode

[jrysana]

I was playing around with #9 locally today and it seemed that a tab for indentation in a code block caused the box drawing in print mode to miscalculate the width of that line, forcing the right border of the box onto a new line in my terminal.

We should probably preprocess tabs out of code blocks and replace them with a couple spaces each or something before printing happens.