metadata-2 (#2273)

Initial implementation of draft/metadata-2

irc/help.go

@@ -339,6 +339,12 @@ command is processed by that server.`,
 MARKREAD updates an IRCv3 read message marker. It is not intended for use by
 end users. For more details, see the latest draft of the read-marker
 specification.`,
+	},
+	"metadata": {
+		text: `METADATA <target> <subcommand> [<everything else>...]
+		
+Retrieve and meddle with metadata for the given target.
+Have a look at https://ircv3.net/specs/extensions/metadata for interesting technical information.`,
 	},
 	"mode": {
 		text: `MODE <target> [<modestring> [<mode arguments>...]]