Adds support for message object returned by the api when executing a webhook.

Created by: Kiritsu

Summary

It was not possible to get the message object when you execute a webhook.

Details

As told in the official discord docs, it is possible to add the querystring parameter wait to get as a response, the message object after the execution of the webhook.

This pull request also fixes the fact that when you pass a null file_name (default param) to one of the overloads, it was trying to add a null key to a dictionary.

Notes

It was tested and worked.