Applied animation effect to the keys if clicked.
Correctly place the key to the center of the selected cell during animation effect.
After the solution of a cell is filled, clear the selected cell.
Fade in the board and keys at the startup.
The board appears from top at the startup as if someone tosses you a sudoku puzzle.
Updated README: trade-offs and file structures. Broke down views by components.
Merge branch 'effect'