Remove completed todo item.
Improve dotfile backup functionality.

First of all the date suffix actually prints the date now. Secondly the
function doesn't attempt to stupidly try to rename files that aren't
there. Although doing this and catching the exception might be a more
sensible way of doing things.
Be a bit more informative when identifying things.
Use appropriate and informative exceptions.
Use a try/except block instead of checking for file existence.