Private serde fork (#390)

* Fork serde_urlencoded

* Apply enum PR https://github.com/nox/serde_urlencoded/pull/30

* Add test to verify enum in query

* Docs are updated to show example of how to use enum.

src/lib.rs

@@ -133,7 +133,6 @@ extern crate num_cpus;
 #[macro_use]
 extern crate percent_encoding;
 extern crate serde_json;
-extern crate serde_urlencoded;
 extern crate smallvec;
 #[macro_use]
 extern crate actix as actix_inner;
@@ -152,6 +151,7 @@ extern crate openssl;
 #[cfg(feature = "openssl")]
 extern crate tokio_openssl;
 
+mod serde_urlencoded;
 mod application;
 mod body;
 mod context;