Remove dependency on `Conduit` from Async
Remove the Client/Server variants from the Conduit interface.

They should instead live in the backends, where they can vary
depending on the specific interpretations desired.
Adapt to moving the type definitions into the backends.

Temporarily unhooks the resolver interfaces in favour of an explicit
connection-management interface.
Rename all the modules to be prefixed by `Conduit_` to follow cohttp

This follows the same convention as Cohttp, but also helps ensure
there's no module namespace clash with generic names such as
`Lwt_unix_net` that other packages might use.
Lift the end point resolution into Lwt_unix directly