Add clippy lints, action some clippy items

src/sync/wait_condition.rs

@@ -31,7 +31,7 @@ impl WaitCondition {
             let context_lock = {
                 let contexts = context::contexts();
                 let context_lock = contexts.current().expect("WaitCondition::wait: no context");
-                context_lock.clone()
+                Arc::clone(&context_lock)
             };
 
             {

src/sync/wait_map.rs

@@ -33,7 +33,7 @@ impl<K, V> WaitMap<K, V> where K: Clone + Ord {
 
     pub fn receive_any_nonblock(&self) -> Option<(K, V)> {
         let mut inner = self.inner.lock();
-        if let Some(key) = inner.keys().next().map(|key| key.clone()) {
+        if let Some(key) = inner.keys().next().cloned() {
             inner.remove(&key).map(|value| (key, value))
         } else {
             None