Feature request: add WARC output option

[midaspt]

Hi @ll.

I have been using monolith more and more for webpage capture but couldn't find a way to make downloads in WARC format (as documented at https://iipc.github.io/warc-specifications/specifications/warc-format/warc-1.0/).

I believe such an option would greatly enhance the reach of monolith as a general purpose utility.

Anyways thanks for your great work as it is. 😎