[board] Clean up a handful of things in position.rs

- Remove unused std::fmt::Write import
- Refer to the piece! macro with $crate (I didn't know this was legal??)
- Remove the doc comments on Position::flags
- Remove {set,clear}_player_has_right_to_castle_flag
- Remove an extraneous local variable from Position::place_piece()

board/src/position/position.rs

@@ -9,7 +9,6 @@ use crate::{
 };
 use std::cell::OnceCell;
 use std::fmt;
-use std::fmt::Write;
 
 /// A lateral side of the board relative to the player. Kingside is the side the
 /// player's king starts on. Queenside is the side of the board the player's
@@ -23,7 +22,7 @@ pub(crate) enum BoardSide {
 macro_rules! position {
     [$($color:ident $shape:ident on $square:ident,)*] => {
         $crate::Position::from_iter([
-            $(piece!($color $shape on $square)),*
+            $($crate::piece!($color $shape on $square)),*
         ].into_iter())
     };
 }
@@ -31,14 +30,6 @@ macro_rules! position {
 #[derive(Clone, Eq, PartialEq)]
 pub struct Position {
     color_to_move: Color,
-
-    /// Position flags indicating various bits of game state.  The flags are as
-    /// follows:
-    ///
-    /// 0. white can castle king-side
-    /// 1. white can castle queen-side
-    /// 2. black can castle king-side
-    /// 3. black can castle queen-side
     flags: Flags,
 
     /// Composite bitboards for all the pieces of a particular color.
@@ -131,15 +122,6 @@ impl Position {
         self.flags.player_has_right_to_castle(color, side)
     }
 
-    fn set_player_has_right_to_castle_flag(&mut self, color: Color, side: BoardSide) {
-        self.flags.set_player_has_right_to_castle_flag(color, side);
-    }
-
-    fn clear_player_has_right_to_castle_flag(&mut self, color: Color, side: BoardSide) {
-        self.flags
-            .clear_player_has_right_to_castle_flag(color, side);
-    }
-
     pub fn place_piece(&mut self, piece: Piece, square: Square) -> Result<(), PiecePlacementError> {
         let type_bb = self.bitboard_for_piece_mut(piece);
 
@@ -149,8 +131,8 @@ impl Position {
 
         type_bb.set_square(square);
 
-        let color_bb = &mut self.bitboard_for_color_mut(piece.color());
-        color_bb.set_square(square);
+        self.bitboard_for_color_mut(piece.color())
+            .set_square(square);
 
         Ok(())
     }