When a king is in check do not allow illegal moves

[RobStallion]

Need to create logic that checks if a king is in check.

If so it restricts the possible moves that other pieces can make so that it only allows moves that either:

• block the check
• capture the piece giving check
• move the king out of check

[RobStallion]

I need to think about this logic in a little more detail but it maybe be good to have check and doubleCheck saved in the state somewhere.

If a king is in double check the only way out is to move the king. If there is an option somewhere that says doubleCheck: True (for example), this may be more efficient than needlessly looking for another pieces possible moves when it will not have any.