Link to http.gml

As soon as the function keyword and structs were announced for GameMaker 2.3, I wrote the first version of this library. This is a wrapper around the http_request function that allows you to ignore the HTTP async event and instead use various callback functions instead.

Includes functions for automatic HTTP request body parsing, including applying a correct Content-Type header, a FormData constructor that can be used to build application/form-data HTTP requests, and hooks for adding HTTP response parsers.