Update gems, add and configure rubocop.
Address rubocop lint issues.
Begin chapter nine.
Fix rubocop guard config.
Update gems again. Remove unsolved problems. Add readme.
Complete exercises for chapter nine.
Significant refactor of chapter eight problem 6 (jigsaw).
Applied null object pattern to pieces/edges to simplify finding
pieces that fit in a spot to fill for the solve algorithm.
Not sure why I got the ordering of columns and rows mixed up.
Fix ordering of rows and columns. Doh.