Add twitch whisper event

This adds the whisper event for whisper messages sent via twitch.
Whisper messages are done via the twitch command "WHISPER" and have the
target (i.e. the client this socket is connected as) and the message as
parameters. Sending a whisper works a little different from normal IRC
as well. You have to send a message to the "#jtv" channel with the
format "/w <target_username> <message>".

src/main/java/org/kitteh/irc/client/library/feature/twitch/TwitchListener.java

@@ -36,6 +36,7 @@
 import org.kitteh.irc.client.library.feature.twitch.event.RoomStateEvent;
 import org.kitteh.irc.client.library.feature.twitch.event.UserNoticeEvent;
 import org.kitteh.irc.client.library.feature.twitch.event.UserStateEvent;
+import org.kitteh.irc.client.library.feature.twitch.event.WhisperEvent;
 import org.kitteh.irc.client.library.feature.twitch.messagetag.Badges;
 import org.kitteh.irc.client.library.feature.twitch.messagetag.BanDuration;
 import org.kitteh.irc.client.library.feature.twitch.messagetag.BanReason;
@@ -173,6 +174,25 @@ public void userState(ClientReceiveCommandEvent event) {
         this.client.getEventManager().callEvent(new UserStateEvent(this.client, event.getOriginalMessages(), this.getChannel(event)));
     }
 
+    @CommandFilter("WHISPER")
+    @Handler(priority = Integer.MAX_VALUE - 2)
+    public void whisper(ClientReceiveCommandEvent event) {
+        if (event.getParameters().size() < 2) {
+            this.client.getExceptionListener().queue(new KittehServerMessageException(event.getOriginalMessages(), "WHISPER didn't contain enough parameters"));
+            return;
+        }
+
+        if (!(event.getActor() instanceof org.kitteh.irc.client.library.element.User)) {
+            this.client.getExceptionListener().queue(new KittehServerMessageException(event.getOriginalMessages(), "Received WHISPER from non-user"));
+            return;
+        }
+
+        final String target = event.getParameters().get(0);
+        final String message = event.getParameters().get(1);
+        final org.kitteh.irc.client.library.element.User sender = (org.kitteh.irc.client.library.element.User) event.getActor();
+        this.client.getEventManager().callEvent(new WhisperEvent(this.client, event.getOriginalMessages(), sender, target, message));
+    }
+
     @Nonnull
     private Channel getChannel(ClientReceiveCommandEvent event) {
         Optional<Channel> channel = this.client.getChannel(event.getParameters().get(0));

src/main/java/org/kitteh/irc/client/library/feature/twitch/event/WhisperEvent.java

@@ -0,0 +1,55 @@
+/*
+ * * Copyright (C) 2013-2018 Matt Baxter https://kitteh.org
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy,
+ * modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.kitteh.irc.client.library.feature.twitch.event;
+
+import org.kitteh.irc.client.library.Client;
+import org.kitteh.irc.client.library.element.ServerMessage;
+import org.kitteh.irc.client.library.element.User;
+import org.kitteh.irc.client.library.event.user.PrivateMessageEvent;
+
+import javax.annotation.Nonnull;
+import java.util.List;
+
+/**
+ * Fires when a whisper is received via twitch.
+ */
+public class WhisperEvent extends PrivateMessageEvent implements TwitchSingleMessageEvent {
+    /**
+     * Creates the event.
+     *
+     * @param client client for which this is occurring
+     * @param originalMessages original messages
+     * @param sender who sent it
+     * @param target who received it
+     * @param message message sent
+     */
+    public WhisperEvent(@Nonnull Client client, @Nonnull List<ServerMessage> originalMessages, @Nonnull User sender, @Nonnull String target, @Nonnull String message) {
+        super(client, originalMessages, sender, target, message);
+    }
+
+    @Override
+    public void sendReply(@Nonnull String message) {
+        this.getClient().sendMessage("#jtv", "/w " + this.getActor().getNick() + " " + message);
+    }
+}