implement formatting for game errors

src/game.rs

@@ -4,6 +4,8 @@ use std::str::FromStr;
 use std::collections::HashMap;
 use std::borrow::BorrowMut;
 use crate::image::Image;
+use std::fmt;
+use std::fmt::Display;
 
 /// in very early versions of Bitsy, room tiles were defined as single alphanumeric characters -
 /// so there was a maximum of 36 unique tiles. later versions are comma-separated.
@@ -77,6 +79,18 @@ pub enum NotFound {
     Tile,
 }
 
+impl Display for NotFound {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f,"Not found: {} data", match self {
+            &NotFound::Anything => "game",
+            &NotFound::Avatar   => "avatar",
+            &NotFound::Room     => "room",
+            &NotFound::Sprite   => "sprite",
+            &NotFound::Tile     => "tile",
+        })
+    }
+}
+
 #[derive(Clone, Debug, PartialEq)]
 pub struct Game {
     pub name: String,