to TLSv1.2.
 *  New: `Request.tag()` permits multiple tags. Use a `Class<?>` as a key to identify tags. Note
    that `tag()` now returns null if the request has no tag. Previously this would return the
    request itself.
 *  New: `Headers.Builder.addAll(Headers)`.
 *  New: `ResponseBody.create(MediaType, ByteString)`.
 *  New: Embed R8/ProGuard rules in the jar. These will be applied automatically by R8.

 *
 * Usually a webserver is reachable with multiple identifiers: its IP addresses, registered
 * domain names, and even `localhost` when connecting from the server itself. Each of a web server's
 * names is a distinct URL and they are not interchangeable. For example, even if
 * `http://square.github.io/dagger` and `http://google.github.io/dagger` are served by the same IP