WIP: build docs from 2.0 dev branches

[davepagurek]

I wanted to check out what the docs looked like for Garima's PR before merging, and these are the changes I had to make to make that happen:

• It builds the docs from npm run build instead of running yuidoc (this should apply to all 2.0 branches)
• For forks, I have to update the repo URL and branch
• For forks, I also have to make a custom build of p5 (running npm run build in the p5 directory), copy that to public/, and then change the URL used in code frames in the site

Eventually I want to make this process easier and more automatic via a command. For now I'm just going to leave this up as a draft PR for reference.