feat(uri): redesign RequestUri type into Uri

Closes #1000

BREAKING CHANGE: The name of `RequestUri` has changed to `Uri`. It is no
  longer an `enum`, but an opaque struct with getter methods.

src/lib.rs

@@ -41,7 +41,6 @@ pub use http::{Body, Chunk};
 pub use method::Method::{self, Get, Head, Post, Delete};
 pub use status::StatusCode::{self, Ok, BadRequest, NotFound};
 pub use server::Server;
-pub use uri::RequestUri;
 pub use version::HttpVersion;
 
 macro_rules! unimplemented {