feat(client): expose connect types without proto feature (#2377)

Make it possible to refer to Connected, Connection, HttpConnector, etc.
without enabling either of the http1/http2 features. This makes feature
selection work better for downstream libraries like hyper-openssl, which
don't want to commit to any particular protocol.

Fix #2376.

src/client/pool.rs

@@ -10,7 +10,7 @@ use futures_channel::oneshot;
 #[cfg(feature = "runtime")]
 use tokio::time::{Duration, Instant, Interval};
 
-use super::Ver;
+use super::client::Ver;
 use crate::common::{task, exec::Exec, Future, Pin, Poll, Unpin};
 
 // FIXME: allow() required due to `impl Trait` leaking types to this lint