Add docs in to master

[jaredly]

You can set github pages to build off of the docs/ folder in master, and
it's a lot less hassle (imo) than maintaining a separate gh-pages
branch.

You can see it rendered here https://jaredforsyth.com/reprocessing/index.html

[Schmavery]

I thought about doing this (it's definitely easier!) but was slightly concerned with the thought of adding several mbs of generated js to our package install. Can you check how big the docs folder is? (Hard to see in github)

Probably the better answer is that I should just accept this and then move forward with publishing to npm with an .npmignore that excludes it.