rfc-bibtex: init at 2.2.1

Generate bibtex entries from IETF rfc/drafts, for instance:
$ rfcbibtex RFC5246 draft-ietf-tls-tls13-21

@techreport{RFC5246,
  author = {T. Dierks and E. Rescorla},
  title = {{The Transport Layer Security (TLS) Protocol Version 1.2}},
  howpublished = {Internet Requests for Comments},
  type = {RFC},
  number = {5246},
  year = {2008},
  month = {August},
  issn = {2070-1721},
  publisher = {RFC Editor},
  institution = {RFC Editor},
  url = {http://www.rfc-editor.org/rfc/rfc5246.txt},
  note = {\url{http://www.rfc-editor.org/rfc/rfc5246.txt}},
}

@techreport{I-D.ietf-tls-tls13,
  author = {Eric Rescorla},
  title = {{The Transport Layer Security (TLS) Protocol Version 1.3}},
  howpublished = {Working Draft},
  type = {Internet-Draft},
  number = {draft-ietf-tls-tls13-21},
  year = {2017},
  month = {July},
  institution = {IETF Secretariat},
  url = {http://www.ietf.org/internet-drafts/draft-ietf-tls-tls13-21.txt},
  note = {\url{http://www.ietf.org/internet-drafts/draft-ietf-tls-tls13-21.txt}},
}