Refactor to create line() function.
Added functions to monitor mouse clicks, and to calculate the grid position for each click, allowing us to draw the proper letter in the proper box.  Also added a 2D array to track the moves that were made, a global variable to track whether it is X or O's turn, and a function to check if either X or O has the win.
Added check for wins across the diagonal.
Added announcement of whether X or O won.
Ensure that only one X or O is put in each square cell.
Add new listener for the 'n' key which triggers restart of a new game.