Add Attachment structure (#1731)

* Add Attachment structure

* Fix linter issues + @private

* Fixed array sends, also added embed sends

* fixed proving path to attachment

* fixed incorrect name assumption from path

* linting fix

* ;)

* im really good at this

* changes as requested by gus

and computer from #1459

* am a dum

* update webhook#send

* readonly addition to getters

* i... uh... oops

* farming deez commits

* fix webhook split

* removed some ugly

* removed .every checks

src/index.js

@@ -26,6 +26,7 @@ module.exports = {
   splitMessage: Util.splitMessage,
 
   // Structures
+  Attachment: require('./structures/Attachment'),
   Channel: require('./structures/Channel'),
   ClientUser: require('./structures/ClientUser'),
   ClientUserSettings: require('./structures/ClientUserSettings'),