Use Error::source() and drop Error::description()

Author: Harald Hoyer <harald@redhat.com>
Author: Paul Colomiets <paul@colomiets.name>

This is revised PR #45

Author: tailhook

examples/context.rs

@@ -1,19 +1,14 @@
-#[macro_use(quick_error)] extern crate quick_error;
-
-use std::io::{self, stderr, Read, Write};
-use std::fs::File;
+use quick_error::{quick_error, ResultExt};
 use std::env;
+use std::fs::File;
+use std::io::{self, stderr, Read, Write};
 use std::num::ParseIntError;
 use std::path::{Path, PathBuf};
 
-use quick_error::ResultExt;
-
 quick_error! {
     #[derive(Debug)]
     pub enum Error {
-        NoFileName {
-            description("no file name specified")
-        }
+        NoFileName {}
         Io(err: io::Error, path: PathBuf) {
             display("could not read file {:?}: {}", path, err)
             context(path: &'a Path, err: io::Error)