Pass array of available moves to UserPrompter
Rename some Board methods, start to add winnable? method
Change board_with_scores method to assign_score
Removing accidentally-created file...
Add spec_helper.rb so minimax_spec can use place_many
Separate tests for winning/losing move
Move current_char method from Game to Board
Refactoring
Change Minimax.get_move to take available positions as a parameter
Change back to passing board instead of available positions

Since Minimax and UserPrompter need to have the same interface, I'm
passing them both the full board instead of just the available positions.
The available positions is enough to decide a human's move (since it
just needs to check that the position is empty), but the Minimax needs
to know what the rest of the board looks like.  Since the board class
has an available_positions method, the UserPrompter just needs to use that.
Start to actually implement assign_score
Remove winnable? method from board and add other_char
Start over Minimax so it only has a Single Responsibility
Separate Player into HumanPlayer and ComputerPlayer

I am moving Minimax#get_move into the Player class, but I was running
into issues because if I do that, the Minimax and UserPrompter classes
wouldn't have the same interface.  Minimax#assign_scores returns an array
of scores, but it will be up to the ComputerPlayer class to pick the
highest one.  The other way I could have done this was to cast the return
value of the move_decider as an array and take the max (I didn't want to do
that because when UserPrompter returns an integer, I would have to convert
it from int to array back to int).
Refactor, remove unnecessary tests/variables
First two tests for Minimax
First working version of minimax algorithm