Add doccomments to irc_message.mli

Signed-off-by: John Else <john.else@citrix.com>
Add module-level doccomments

Signed-off-by: John Else <john.else@citrix.com>
Tidy doccomments

Signed-off-by: John Else <john.else@citrix.com>
Add more doccomments to irc_message.mli

Signed-off-by: John Else <john.else@citrix.com>
Replace Irc_message.parse_result with a generic Irc_result.t

Signed-off-by: John Else <john.else@citrix.com>