Add 'FromFen' trait

src/fen.rs

@@ -0,0 +1,6 @@
+/// A trait to mark items that can be converted from a FEN input.
+pub trait FromFen: Sized {
+    type Err;
+
+    fn from_fen(s: &str) -> Result<Self, Self::Err>;
+}

src/lib.rs

@@ -1,3 +1,4 @@
 pub mod board;
+pub mod fen;
 pub mod movegen;
 pub mod utils;