Check if knight move is valid

[k4pran]

https://github.com/ryanmccauley211/Chess-2.0/blob/10380174e7cefce93786f8724e90bd1de910cd0f/src/com/neueda13/Move.java#L5-L38

Game board will include where all pieces are, board size etc. Determine if a move to a given position is valid given the current game board's state and the units position/abilities.

• Return true if knight's move is valid