Hey, I apologize for the delay. Currently, documentation in HTML format is only available online. However, HTML documentation is generated automatically from the JSDoc comments on the Gamemaker script itself (above each function/method), using another tool I wrote named GMLDocMaker. So, this means that all documentation is essentially inside the gooey script. You can use the find functionality (or middle click a function name in Gamemaker) and it will show you the explanation.
If you still need the offline documentation I could try to generate an offline version in a format like PDF or so. It won't be pretty, but it might work.
Let me know if I can further help!