Only minor details in the internals of the `h2` module needed tweaking
for migrating onto the latest version -- `HttpConnect` implementations
are now required to return an error type that implements an
`HttpConnectError` trait.
BREAKING CHANGE: Server::https was changed to allow any implementation
of Ssl. Server in general was also changed. HttpConnector no longer
uses SSL; using HttpsConnector instead.
Connector::connect already used &self, and so would require
synchronization to be handled per connector anyway. Adding Sync to the
Client allows users to setup config for a Client once, such as using a
single connection Pool, and then making requests across multiple
threads.
Closes#254
BREAKING CHANGE: Connectors and Protocols passed to the `Client` must
now also have a `Sync` bounds, but this shouldn't break default usage.
