started moving some of the user interface into its own UI class
removed commented out code
moved Board#show to UI class as UI.show_board
moved 'Executing computer move' into a generic output method in the UI class.
fixed human_input method which wasn't working; it allowed you to make invalid moves
Board#mark method no longer needs to check or valid input
now that  Board#show is in UI.show_board, respective changes were made to board_spec and ui_spec
Merge pull request #2 from kelmerp/ui

Ui