other stuff to do
  1. The calculator portion does not work for big numbers, i.e. where
    one can type in math operations and see the abacus perform, e.g.
    5,000,000,000,000,000.0+1.
  2. When displayBase != base calculate with strings instead of
    "long long".  I.e. the number of rails can be large if displayBase =
    base, but may error out when this is not true for a large number of
    rails.
  3. Allow for locale to use "," for "." and vice versa.
    It might be confusing to change this if one actually wanted to try
    different locales, e.g. Danish Abacus.
    http://www.acm.uiuc.edu/webmonkeys/book/c_guide/2.6.html
  4. Handling of negatives would be nice (work started with complement
    function).
  5. "Teach" has beads and rail highlighted to make clear the current
    position of calculation for digit; should this be extended to highlight
    a printed digit?
