Update sunkMap book-keeping
Update sunkMap book-keeping

 - Sink will now first check for sunkMap to make sure that the ship is not already sunk.
 - Raise will enable each sunken ship square after setting all their statuses to HIT
 - Raise will remove ship from sunkMap

Signed-off-by: Shen Yichen <be3bb257ef8d73236feaba36cd3e5ee9095e6819@gmail.com>

yichenshen/Battleships