added

Merge(int i1, int c1, int i2, int c2, char dir)
this method merges two tiles in the direction indicated by dir
This method will be called by KeyPressed(KeyEvent e) with the correct direction.
Once the required changes have been made, UIM will be called to update the UI.

addTile()
 Adds a Tile to a random empty location. Called by KeyPressed(KeyEvent e)