Implement outbound PPv2

This mirrors #11

This is a proxy forwarder protocol primary used by layer 4 proxies to forward information about the original client such as their IP. It does so by pre-pending the connection stream with a text or binary formatted blob of data. It's more efficient than adding X-Forwarded-For and similar headers to every request.

In HttpClient this would be implemented at the proposed Dialer or Bedrock layer, sending the blob just after the connection was established.