Stub outline
Started with the stub Facia implementation

This will form the basis of the public API. At the moment it just uses
the Facia JSON, but the fronts team will likely change this so it has
lots of their logic in this library.
Out of date comment, might as well just remove it

`demo.sc` is useful for documenting the behaviour...
Tidy up file structure a little
Tidy Facia stuff, improve Response and update demo
Fleshed out Facia logic and started adding CAPI stuff

We can now fetch intermediate Facia data for a collectiion and then
enhance it with the extra metadata from the fronts config json.

Began to work on the Content API side of things - hydrating the Facia
IDs and performing backfill queries.
Overhaul ApiError

The previous type was more appropriate to an HTTP API than a client
library. This one makes a bit more sense.
Start / stub CAPI tests