Add some convenience DSL methods

lila/src/main/scala/model/Board.scala

@@ -5,6 +5,8 @@ import Pos._
 
 case class Board(pieces: Map[Pos, Piece], taken: List[Piece] = Nil) {
 
+  def apply(at: Pos): Option[Piece] = pieces get at
+
   def place(piece: Piece) = new {
     def at(at: Pos): Valid[Board] =
       if (pieces contains at) failure("Cannot move to occupied " + at)

lila/src/main/scala/model/Piece.scala

@@ -9,7 +9,9 @@ case object Bishop extends Role
 case object Knight extends Role
 case object Pawn extends Role
 
-sealed trait Color
+sealed trait Color {
+  def /(role: Role) = Piece(this, role)
+}
 case object White extends Color
 case object Black extends Color