Made several changes

Changed logic when computers turn to determine if a jump is present from
toCoordX, Y +/- 1 to fromCoordX, Y +/- 2. This stops the computer from
saying there is a jump when there really isn't one.
Also added 2 else's inside of human_move. Without these here, when the
player is a king, they can accidentally mistype the square they want to
go to without any invalid move being raised. This allows the computer to
take an extra turn.

Please check over these changes and make sure you don't get any weird
bugs because of it.