Merge pull request #9 from bsamseth/king-move

Fix #7, King move rules implemented (without castling)
Fix #8, bishops can now move only as they should.
Merge pull request #10 from bsamseth/B-N-move-bug

Fix #8, bishops can now move only as they should.
Fix #6, fix bug whit knights jumping accros the board.
Merge branch 'B-N-move-bug' into master
Add method RuleBook#castlingMove that decides if s1-s2 is legal for castling. King can castle, but rook needs to be moved (unsolved)