Add support for /kill

Fixes #3122

src/client.js

@@ -53,6 +53,7 @@ const inputs = [
 	"ignore",
 	"invite",
 	"kick",
+	"kill",
 	"mode",
 	"nick",
 	"notice",

src/plugins/inputs/kill.js

@@ -0,0 +1,11 @@
+"use strict";
+
+exports.commands = ["kill"];
+
+exports.input = function({irc}, chan, cmd, args) {
+	if (args.length !== 0) {
+		irc.raw("KILL", args[0], args.slice(1).join(" "));
+	}
+
+	return true;
+};