Support multi-prefix NAMES/WHO replies
Document STARTTLS numerics
Support plaintext IPv4/v6 addresses

Also stop converting filenames/addresses into objects. Higher-level code
should deal with the case of invalid input.
Add some comments for IRCSupport::Message#type
Make sure all predicate methods return a boolean
Simplify code to determine message type
Use a simpler command -> class/type mapping

PRIVMSG, NOTICE, and CTCP ACTION are not grouped together anymore.
Fix some YARD comments
Add another test for CTCP ACTION
Support extended-join
Add missing #public? method for Privmsg
Code cleanup
Unescape backslashes in DCC filenames