05/01/99 - Added "backup" pseudo-rule to allow for correcting mistakes.
         - Wrote simple lexer to avoid having to use flex.  This one
           uses C++ input streams much more cleanly.
         - Prettified some of the .h and .cc files with comments.
8/14/99, 11:02 PM -- Trying to add support for "hidden" axioms.  Problem: Proof:applyRule does not properly apply axioms (add to lhs).