Add metadata to PDF

[PeterNerlich]

This PR writes common PDF metadata as specified in the title page information:

• Title
• Subject
• Author
• Keywords
• Lang

I wanted to just write everything in the title page as custom metadata, but that would require some light hacking of reportlab

[vilcans]

That's useful! Though I didn't find official documentation from Adobe or Reportlab about what the metadata fields are, but Google's AI said:

• Creator: The software or application used to create the original document (e.g., Microsoft Word, Google Docs).
• Producer: The tool used to convert the document into a PDF (e.g., Acrobat Distiller).

So, I think those two fields should not be included. Both these fields are supposed to be name of software, while in the metadata of a screenplay you'd expect them to refer to people.

[PeterNerlich]

Yes, that's reasonable. I removed those