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/webhook.js

@@ -0,0 +1,10 @@
+const fs = require('fs');
+
+module.exports = {
+  category: 'Examples',
+  name: 'Webhooks',
+  data:
+`\`\`\`js
+${fs.readFileSync('./docs/custom/examples/webhook.js').toString('utf-8')}
+\`\`\``,
+};