Snake now keyboard controllable

  * Can move up, down, left right with arrow keys
  * canvas repaints the white background every frame
  * how the movement works:
    * button is pushed
    * x or y coordinate is incremented based on the key
    * tail is popped off of the snake
    * tail is assigned the head's new coordinates
    * tail is unshifted onto the snake
Add "game over" logic

  * If snake hits the bounds, the game is over
  * Right now, just ends the game
  * Page must be reloaded to start again
Merge pull request #3 from mknudsen01/game-over-clause

Game over clause