Merge pull request #39 from yanns/remove_mut_ref

AtomicUsize does not need a mutable reference to be increment

Author: tailhook

examples/threaded_with_shared_counter.rs

@@ -21,12 +21,12 @@ struct Context {
 }
 
 trait Counter {
-    fn increment(&mut self);
+    fn increment(&self);
     fn get(&self) -> usize;
 }
 
 impl Counter for Context {
-    fn increment(&mut self) { self.counter.fetch_add(1, Ordering::SeqCst); }
+    fn increment(&self) { self.counter.fetch_add(1, Ordering::SeqCst); }
     fn get(&self) -> usize { self.counter.load(Ordering::SeqCst) }
 }