Implement std::fmt::Display for the error types

examples/show.rs

@@ -1,9 +1,12 @@
 extern crate libnotify;
 
 fn main() {
-    let notify = libnotify::Context::new("hello").unwrap();
+    let notify = libnotify::Context::new("hello").unwrap_or_else(|e| {
+        panic!("{}", e);
+    });
+    let body_text = Some("This is the optional body text.");
     let n = notify.new_notification("This is the summary.",
-                                    Some("This is the optional body text."),
-                                    None).unwrap();
-    n.show().unwrap();
+                                    body_text,
+                                    None).unwrap_or_else(|e| panic!("{}", e));
+    n.show().ok().expect("Failed to show notification");
 }

src/lib.rs

@@ -17,6 +17,7 @@ extern crate "glib-2_0-sys" as glib;
 
 use std::ffi::CString;
 use std::marker::PhantomData;
+use std::fmt;
 
 use glib::types::{
     TRUE,
@@ -32,12 +33,33 @@ pub enum ContextCreationError {
     NulError
 }
 
+impl fmt::Display for ContextCreationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        use ContextCreationError::*;
+        match *self {
+            AlreadyExists => write!(f, "A Libnotify context already exists."),
+            InitFailure => write!(f, "Failed to initialize libnotify."),
+            NulError => write!(f, "Argument contains a nul character.")
+        }
+    }
+}
+
 #[derive(Debug)]
 pub enum NotificationCreationError {
     NulError,
     Unknown
 }
 
+impl fmt::Display for NotificationCreationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        use NotificationCreationError::*;
+        match *self {
+            NulError => write!(f, "Argument contains a nul character."),
+            Unknown => write!(f, "Unknown error")
+        }
+    }
+}
+
 /// The context which within libnotify operates.
 ///
 /// Only one context can exist at a time.