feat(all): add socket timeouts

Methods added to `Client` and `Server` to control read and write
timeouts of the underlying socket.

Keep-Alive is re-enabled by default on the server, with a default
timeout of 5 seconds.

BREAKING CHANGE: This adds 2 required methods to the `NetworkStream`
  trait, `set_read_timeout` and `set_write_timeout`. Any local
  implementations will need to add them.

src/server/request.rs

@@ -66,18 +66,11 @@ impl<'a, 'b: 'a> Request<'a, 'b> {
     }
 
     /// Set the read timeout of the underlying NetworkStream.
-    #[cfg(feature = "timeouts")]
     #[inline]
     pub fn set_read_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
         self.body.get_ref().get_ref().set_read_timeout(timeout)
     }
 
-    /// Set the read timeout of the underlying NetworkStream.
-    #[cfg(not(feature = "timeouts"))]
-    #[inline]
-    pub fn set_read_timeout(&self, _timeout: Option<Duration>) -> io::Result<()> {
-        Ok(())
-    }
     /// Get a reference to the underlying `NetworkStream`.
     #[inline]
     pub fn downcast_ref<T: NetworkStream>(&self) -> Option<&T> {