Collate markdown docs into a PDF document with pandoc

[stmio]

Adds a GitHub Action which collates all markdown documentation files into a single PDF doc, see #3 (comment). The action runs on every commit and uses pandoc to generate the document, which outputs the file to GitHub Artifact storage.

The main downside of this document in comparison to the website is that the GIF animations display as static images.

I am happy to maintain this action into the future, let me know if you find any problems. 😄

Closes #3

[dacap]

Hi @stmio, thanks a lot for this PR! I've checked the PDF output and it looks great for a first draft, as you said the main problem with this is not having the GIF animations (one reason I didn't dedicate time to this was that, and we probably will be more video/GIF intensive in the future).

Anyway this can be available in case someone find it useful. I'm not sure if there is a way to sort chapters, but probably "51 Aseprite Help" should be the first one (as it's the overview).

I'll merge it right now. Thanks again!

[stmio]

No problem, thank you! I will have a look into making some improvements soon. 😄

At the moment, the chapters are sorted alphabetically by file name (due to using *.md), followed by the files in ./extensions/ at the end. I'll have a look at adjusting the order.