Add snippet for fmt::Display implementation

vim/neosnippets/rust.snip

@@ -2,3 +2,12 @@ snippet     debug
 abbr        deb
 options     head
     println!("{:?}", ${1});
+
+snippet     impldisplay
+abbr        disp
+options     head
+    impl fmt::Display for ${1} {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "${2}", ${3})
+        }
+    }