Pdfjs

[BryceStevenWilley]

I added the ability to compare PDFs! It's currently one step, I expect the baseline PDF "something-in-sources.pdf" and the new PDF "downloaded.pdf" to be the same, but happy to add more, depending on what we think would be useful for folks.

Making this a draft to make sure the API is as we want it.

In this PR, I have:

• [x] Added tests for any new features or bug fixes (if relevant)
• [x] Added my changes to the CHANGELOG.md at the top, under the "Unreleased" section (still unsure what the final API will look like)
• [x] Ensured issues that this PR closes will be automatically closed

Links to any solved or related issues

Fix #25.

Any manual testing I have done to ensure my PR is working

Just added the automated tests.

[BryceStevenWilley]

Ready for review, addressed all of the comments, and made slight cleanups to the findFiles function, but everything else remained the same!

[plocket]

Add to the changelog if you have a mo