Simplify matching_seat method and conditions passed to it
Cases up to 4:ABCD need no code changes
Add vacate! method to Seat
Change variable naming in best_available_seat
Express "seats on both sides are full" rule more clearly
Implement 4:ABCbBD
No code changes needed up to 4:ABCDabcA
No code changes needed up to 7:FMTOWNS