Made the grid square to clarify area and perimeter puzzles. Fixed a bug where lines were drawing a bit long; the problem was integer division. Made it so that puzzles couldn't be repeated immediately. Made it so that rectangles with area 0 couldn't solve perimeter puzzles, and they return a different feedback message. Displayed row and column numbers on the grid. Closes #5.
Merge branch 'master' of https://github.com/kangareuben/puppyspen