* mutually recursive maybe_continue and async_recv
  functions are really tricky to reason about, but
  it doesn't seem like it makes sense for maybe_continue
  to do error handling at all, since async_recv was already
  doing it
  * maybe_continue and stream_loop shouldn't select
    socket messages
  * we're getting into a state where the socket sends
    us a message while we're doing other things and
    we do that receive and then crash
* this change makes async_recv the only one to do
  a select for transport messages

* When the server closes the connection
  and :ssl sends us :ssl_closed, we weren't
  handling the message, which caused it to leak
  into the mailbox even after the request was ended
  * need to flush to make sure it's gone in this case
    where the server hangs up
  * caused when Connection: close header is sent

fix debugging statement

* bug i think appeared in 6ddc33c
* when streaming the response, we terminate
  the parse recursive calls early since
  there is no match for {:more, {hparser, ...:on_trailers...}}
  case