fix(lib): Remove unused unimplemented! macro.

This macro isn't used anywhere, std now has an unimplemented macro
if we want to use it, and the nightly compiler now warns that this
unused.  This warning is a failure when compiling tests.

src/lib.rs

@@ -46,18 +46,6 @@ pub use status::StatusCode::{self, Ok, BadRequest, NotFound};
 pub use server::Server;
 pub use version::HttpVersion;
 
-macro_rules! unimplemented {
-    () => ({
-        panic!("unimplemented")
-    });
-    ($msg:expr) => ({
-        unimplemented!("{}", $msg)
-    });
-    ($fmt:expr, $($arg:tt)*) => ({
-        panic!(concat!("unimplemented: ", $fmt), $($arg)*)
-    });
-}
-
 #[cfg(test)]
 mod mock;
 pub mod client;