Need lots of quit options

Several areas in program where you can get stuck in imput if you don't input the correct thing. Need to implement exits to program at all, or at least frequent, IO breaks.

Start by locating the program's input-handling loops and enumerate the areas where invalid input can leave users stuck. Define the exit behavior for each affected prompt, then verify that users can quit from all identified interaction points without breaking normal Battleship gameplay.

Written by the indexing model from the issue text.