Can now move pieces

Sources/Engine/Pieces/Piece.swift

@@ -69,8 +69,28 @@ public class Piece {
 		return []
 	}
 	internal var delegate: EventDelegate?
-	internal func move(to dst: Square.Position) {}
-	internal func isLegal(on pos: Square.Position) -> Bool { false }
+	internal func move(to dst: Square.Position) throws {
+		if !(legalPositions.contains { $0 == dst }) {
+			throw Board.MoveFailure.destinationIsIllegal(pos: dst)
+		}
+
+		try delegate?.movePiece(self, to: dst)
+	}
+	internal func isLegal(on pos: Square.Position) -> Bool {
+
+		if let board = board, let s = board[pos] {
+			if let p = s.piece {
+				if p.color == color { return false }
+				if p.kind == .King {
+					// TODO: Notify board of check
+					delegate?.notify(.kingInCheck(self))
+					return false
+				}
+			}
+
+		}
+		return true
+	}
 
 	internal init(kind: Kind, on pos: Square.Position, with col: Color) {
 		self.kind = kind