Add 'TryInto<Square>' for 'Bitboard'

src/board/bitboard/error.rs

@@ -0,0 +1,19 @@
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum IntoSquareError {
+    /// The board is empty.
+    EmptyBoard,
+    /// The board contains more than one square.
+    TooManySquares,
+}
+
+impl std::fmt::Display for IntoSquareError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let error_msg = match self {
+            Self::EmptyBoard => "The board is empty",
+            Self::TooManySquares => "The board contains more than one square",
+        };
+        write!(f, "{}", error_msg)
+    }
+}
+
+impl std::error::Error for IntoSquareError {}