Implement Display for NSString.

Author: SSheldon

src/string.rs

@@ -1,3 +1,4 @@
+use std::fmt;
 use std::os::raw::{c_char, c_void};
 use std::slice;
 use std::str;
@@ -70,6 +71,12 @@ impl INSCopying for NSString {
     type Output = NSString;
 }
 
+impl fmt::Display for NSString {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self.as_str(), f)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::{INSCopying, INSString, NSString};