Added VoiceStateUpdate handler and DataStore for VoiceChannels. Also added toString methods to Guilds, DMChannels, ServerChannels and Users.

src/structures/datastore/VoiceChannelDataStore.js

@@ -0,0 +1,12 @@
+'use strict';
+
+const AbstractDataStore = require('./AbstractDataStore');
+
+class VoiceChannelDataStore extends AbstractDataStore{
+	constructor() {
+		super();
+		this.register('members');
+	}
+}
+
+module.exports = VoiceChannelDataStore;