refactor(error): remove redundant parts of error names

The old names followed the old style of including the module name and
"Error" in each variant. The new style is to refer to an error from its
owning module, and variants are now scoped to their enum, so there's no
need to include the enum name in the variant name.

BREAKING CHANGE: The terms `Http` and `Error` have been removed from the Error
  type and its variants. `HttpError` should now be accessed as `hyper::Error`,
  and variants like `HttpIoError` should be accessed as `Error::Io`.

src/lib.rs

@@ -149,7 +149,7 @@ extern crate test;
 pub use mimewrapper::mime;
 pub use url::Url;
 pub use client::Client;
-pub use error::{HttpResult, HttpError};
+pub use error::{Result, Error};
 pub use method::Method::{Get, Head, Post, Delete};
 pub use status::StatusCode::{Ok, BadRequest, NotFound};
 pub use server::Server;