add native-tls and serde json support

src/error.rs

@@ -1,5 +1,7 @@
+/// The Errors that may occur when processing a `Request`.
 #[derive(Debug)]
 pub enum Error {
+    /// An HTTP error from the `hyper` crate.
     Http(::hyper::Error),
     #[doc(hidden)]
     __DontMatchMe,
@@ -11,4 +13,5 @@ impl From<::hyper::Error> for Error {
     }
 }
 
+/// A `Result` alias where the `Err` case is `reqwest::Error`.
 pub type Result<T> = ::std::result::Result<T, Error>;