style(all): Address suggestions made by rust-clippy

src/http/h1.rs

@@ -171,8 +171,8 @@ impl HttpMessage for Http11Message {
                         }
                     }
                 };
-                match &head.method {
-                    &Method::Get | &Method::Head => {
+                match head.method {
+                    Method::Get | Method::Head => {
                         let writer = match write_headers(stream, &head) {
                             Ok(w) => w,
                             Err(e) => {
@@ -734,7 +734,7 @@ impl<W: Write> HttpWriter<W> {
 
     /// Access the inner Writer.
     #[inline]
-    pub fn get_ref<'a>(&'a self) -> &'a W {
+    pub fn get_ref(&self) -> &W {
         match *self {
             ThroughWriter(ref w) => w,
             ChunkedWriter(ref w) => w,
@@ -748,7 +748,7 @@ impl<W: Write> HttpWriter<W> {
     /// Warning: You should not write to this directly, as you can corrupt
     /// the state.
     #[inline]
-    pub fn get_mut<'a>(&'a mut self) -> &'a mut W {
+    pub fn get_mut(&mut self) -> &mut W {
         match *self {
             ThroughWriter(ref mut w) => w,
             ChunkedWriter(ref mut w) => w,

src/http/h2.rs

@@ -302,7 +302,7 @@ fn prepare_headers(mut headers: Headers) -> Vec<Http2Header> {
 /// A helper function that prepares the body for sending in an HTTP/2 request.
 #[inline]
 fn prepare_body(body: Vec<u8>) -> Option<Vec<u8>> {
-    if body.len() == 0 {
+    if body.is_empty() {
         None
     } else {
         Some(body)
@@ -322,7 +322,7 @@ fn parse_headers(http2_headers: Vec<Http2Header>) -> ::Result<Headers> {
     }
 
     let mut raw_headers = Vec::new();
-    for &(ref name, ref value) in headers.iter() {
+    for &(ref name, ref value) in &headers {
         raw_headers.push(httparse::Header { name: &name, value: &value });
     }