Documentation js

[bennlich]

This PR replaces jsdoc with documentation.js. I was expecting to write our own theme for documentation.js, but the default theme is actually very good. Importantly, there is now a documentation.yml file, which defines the table of contents.

What I like about documentation.js:

• all docs on a single page, so you can use browser ctrl+f to find things
• the built-in search feature is good (better than the one we were using in jsdoc)
• documentation.yml lets you create categories in the table of contents (see https://github.com/documentationjs/documentation/blob/master/docs/CONFIG.md)
• the default theme is extremely readable

In this PR I also added a few documentation stubs for classes that I think we should aim to document for a first release.

@backspaces let me know what you think!

[backspaces]

I like it! Thanks for digging into this.