Add DeathPlayer

* Chooses targets based on probability square will contain ship.  (Basically, searches outwards from the centre.)
* Avoids firing at previous targets.
Make target selection code more succinct.
Move Ship fns to own module
Pull out ship pos chooser into own module
Pull out ship pos probability into own module
Add Board fn to get coords for line starting from coord
Move target pick code to own fn
Record every shot made
Add module to hunt around hits
Hunt around hits, then try probabilistic shot
Move probability target code to own fn
Rm unnecessary if/else for target strategy selection
Make Board functional module
Rm unused fn
Rm unnecessary selfs
Fix Board.to_s for new functional Board approach
Incorporate board state into probability

* Now does not increment probs for position if ship can't be there because of previous miss on body of ship.
Add Position.to_padded_coordinates fn
Never puts ships next to each other
Merge pull request #2 from maryrosecook/master

DeathPlayer