input: Write a python function to create a chess piece and move it to a specific position.
  assert piece.move(7, 4) == "White piece moved to e8."
  assert piece.move(5, 2) == "White piece already moved!"
  assert piece.move(2, 0) == "White piece already moved!"
output: class ChessPiece:
      def __init__(self, color):
          self.color = color
          self.position = None
  
      def move(self, x, y):
          if self.position is not None:
              return f"{self.color.capitalize()} piece already moved!"
          self.position = (x, y)
          column = chr(ord('a') + y)
          row = 8 - x
          return f"{self.color.capitalize()} piece moved to {column}{row}."
  
  piece = ChessPiece("white")