doc: fix typos in user's guide
doc: use HTML pages for links to RFCs in user's guide
doc: add IRC RFCs for file irc-protocol.c in developer's guide
irc: add missing RFC 2813 in header
relay: add experimental websocket server support (RFC 6455) for irc and weechat protocols, new option relay.network.websocket_allowed_origins

It is a partial implementation of RFC 6455: fragmentation and control frames are
not yet supported.
Text and binary frames are supported.