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/client/voice/VoiceConnection.js

@@ -165,7 +165,7 @@ class VoiceConnection extends EventEmitter {
   }
 
   /**
-   * Set the token and endpoint required to connect to the the voice servers.
+   * Set the token and endpoint required to connect to the voice servers.
    * @param {string} token The voice token
    * @param {string} endpoint The voice endpoint
    * @returns {void}