Proposal: Reorganizing to a WIT-first flow #240

After some discussion at the SIG Docs meeting, I expressed the beginnings of a plan to move to a format for the docs that is WIT-first.

The basic format for guides might start to look like the following:

1. Introduce a WIT interface
2. Satisfy dependencies with tooling (if any)
3. Build language implementation/bindings that satisfy the interface

While (3) is language specific, (1) and (2) are actually not, so it might make sense to reorganize the guide itself so that the first two steps are unified, and the third is broken out by language.

This is a bit hard to grasp conceptually, so the second step to being able to discuss it in this issue is creating a prototype that shows how navigation would change, etc.