[board, core, moves, position] Implement castling

Implement a new method on Position that evaluates whether the active color can castle
on a given wing of the board. Then, implement making a castling move in the position.

Make a new Wing enum in the core crate to specify kingside or queenside. Replace the
Castle enum from the board crate with this one. This caused a lot of churn...

Along the way fix a bunch of tests.

Note: there's still no way to actually make a castling move in explorer.

core/src/coordinates.rs

@@ -1,5 +1,9 @@
 // Eryn Wells <eryn@erynwells.me>
 
+mod wings;
+
+pub use wings::Wing;
+
 use crate::Color;
 use std::fmt;
 use thiserror::Error;
@@ -519,7 +523,7 @@ mod tests {
     fn bad_algebraic_input() {
         assert!("a0".parse::<Square>().is_err());
         assert!("j3".parse::<Square>().is_err());
-        assert!("a11".parse::<Square>().is_err());
+        assert!("a9".parse::<Square>().is_err());
         assert!("b-1".parse::<Square>().is_err());
         assert!("a 1".parse::<Square>().is_err());
         assert!("".parse::<Square>().is_err());