Bug fixes

Fixed "ValueError: depythonifying 'int', got 'NoneType'" when passing
y_move/x_move/z_move None to CGEventCreateScrollWheelEvent.

Fixed typo in scroll_event calls (y_movement should be y_move,
x_movement should be x_move, z_movement should be z_move).
Merge pull request #52 from jhosmer/master

Bug fixes