Added and fixed a bunch of docs stuff (#1767)

- Fixed a common copy paste fail `the the <thing>` in various places
- Apparently I can't type Resolvable correctly,
Fixed that wherever applicable
- Documented GroupDMChannel#nicks so that it will be displayed on the docs
- GroupDMChannel#icon is nullable
- Removed empty InviteOptions typdef, as its properties are now documented in GuildChannel#createInvite
- MessageMentions#channels is no longer nullable
- RoleData#permissions takes a PermissionResolvable or an array of them
- Webhook#avatar is nullable
- Added HTTPOptions typedef and added it to ClientOptions typedef
- ClientUserChannelOverride#muted is for a channel and not a guild directly

src/structures/ClientUserGuildSettings.js

@@ -8,7 +8,7 @@ const ClientUserChannelOverride = require('./ClientUserChannelOverride');
 class ClientUserGuildSettings {
   constructor(data, client) {
     /**
-     * The client that created the instance of the the user
+     * The client that created the instance of the ClientUserGuildSettings
      * @name ClientUserGuildSettings#client
      * @type {Client}
      * @readonly