Started to work on king threats

Sources/Engine/Pieces/King.swift

@@ -1,5 +1,6 @@
 final class King: Piece {
-
+	typealias Threats = (Piece?, Piece?)
+	var threats: Threats = (nil, nil)
 	override var unicodeRepresentation: String {
 		return color == .Black ? "♛" : "♕"
 	}
@@ -17,12 +18,12 @@ final class King: Piece {
 		].filter { $0.index != nil }
 	}
 
-	override var legalPositions: [Square.Position] {
-		return pseudoLegalPositions.filter { isLegal(on: $0) }
-	}
-
 	override func isLegal(on pos: Square.Position) -> Bool {
-		super.isLegal(on: pos)
+		guard super.isLegal(on: pos) else {
+			return false
+		}
+		// Do stuff
+		return true
 	}
 
 	init(with color: Color, on position: Square.Position) {