Add forgotten Knight parsing

rs/src/ui.rs

@@ -115,6 +115,7 @@ impl board::PieceType {
     fn parse(c: char) -> Result<Self, ()> {
         match c {
             'P' => Ok(board::PieceType::Pawn),
+            'N' => Ok(board::PieceType::Knight),
             _ => Err(()),
         }
     }