Cleaned up ShipsGenerator. Removed methods in ShipsGenerator for checking for occupied coordinates. That is handled in Ships#occupied? and Ships#<<() now.

Refactored Ships#hit? and Ships#<< to take advantage of Ships#occupied?
Renamed Guesses.remaining to Guesses.remaining_guesses to clarify its intention.
Still need to figure out why not breaking out of the game loop at end of game. Game should exit- starts new game instead.