adds new WebhookClient and allows you to fetch channel webhooks and such without being "over the top" (#768)

* start blocking out client

* proto webhookclient

* wee working webhooks

* it's all working

* run docs

* fix jsdoc issues

* add example for webhookClient

* add example in the examples place

* fix docs

docs/custom/examples/webhook.js

@@ -0,0 +1,12 @@
+/*
+  Send a message using a webhook
+*/
+
+// import the discord.js module
+const Discord = require('discord.js');
+
+// create a new webhook
+const hook = new Discord.WebhookClient('webhook id', 'webhook token');
+
+// send a message using the webhook
+hook.sendMessage('I am now alive!');