Initial version of PDF extractor

This is my initial efforts on developing a script to extract resource information from PDF files. It uses [PDFMiner](https://euske.github.io/pdfminer/index.html) to turn each PDF into HTML and then does cartwheels with it in BeautifulSoup.

At the end of the day, it tries to tag certain HTML elements with the `rad-category` and `rad-resource` CSS classes. From there, we can do... something with it.

It's by no means complete, but I want to add it so that others can take a look and improve it. It needs a lot of work but I tried to document pretty clearly what it does.