• A bug that prevented trailers (e.g. HEADER frame at the end) to be
  generated in certain cases was fixed. See #233 where it prevented
  gRPC responses to be properly generated.
• :scheme pseudo-header values, not matching the
  connection scheme, are forwarded via absolute uris to the
  http protocol processing to preserve semantics of the request.
  Checks on combinations of pseudo-headers values/absence
  have been added as described in RFC 7540. Fixes #230.
• Fix possible beam bucket double free from session destroy. [ylavic]