TODO: Flesh me out

Caveats:

- No attempt is made to validate that the input for client requests or responses
  are valid according to the HTTP grammar; such cases will fail when rejected by
  the other party.
- Details indicated by RFC 7230 et al as "obsolete" are not implemented
- Max header length including "name: value" is 4KiB

TODO:

- Server stuff
- TLS