Greasy Fork镜像

Removed unnecessary async

Fixed wrong dates (oops)

Changed filename so it doesn't have ".pdf" twice in it.

Studydrive changed their mechanics quite a bit lately, switching from the PDF.js to the proprietary PSPDFKit library. I had to reengineer the script quite a bit and choose another approach to get to the pdf but it seems to be working now.

Made the script a bit more robust by accounting for a timing issue when setting up the download button. I also added a backup download menu option.