Add ability to pass extra kwargs to subprocess

[mgao6767]

This patch allows users to pass extra kwargs to subprocess.check_output in Document.generate_pdf.

It can be useful when, e.g., we want to hide the popup console window in certain circumstances.

self.doc.generate_pdf(
            pathlib.Path(output_path).joinpath(filename),
            compiler_args=["--shell-escape", "-f"],
            check_output_kwargs={"creationflags": subprocess.CREATE_NO_WINDOW},
        )