Split docs into pages as opposed to one long page

Currently all the documentation is on one long page. This was fine initially but now the amount of things we are documenting has outgrown our one pager.

We should split the documentation into multiple pages. This is better for SEO and makes it easier for people to link to different pages. Also currently we are using smaller and smaller headers for each sub-section, which is good because it shows visual hierarchy, but we are nesting so deep that the font sizes are getting super close to the normal text size.

## Inspiration

I really like the [Apollo docs](https://www.apollographql.com/docs/react/features/error-handling.html), they have the same issues we have with regards to catering to different types of users, in their case their split is Client, Engine and Server. I think it would be good to borrow some inspiration from them with regards to our own docs.

[Redux](https://redux.js.org/introduction/learningresources#thinking-in-redux) is another project that has lots of (nested) documentation, they added another navigation on the right side of the page. That could also be an option for us if we'd want to clean up the navigation a bit.

Start by locating the current single documentation page in the Jekyll site and reviewing the Apollo and Redux examples linked in the issue. Define the page grouping and navigation approach before changing content. Done means the documentation is split into linked pages with usable navigation and shallower heading nesting.

Written by the indexing model from the issue text.