adjust implementation state

See merge request !3

Implement basic read-only support for magic-folders

Closes #2

See merge request !2

It was pedagogical

I can't figure out how to make it pass reliably.

SIGNED-OFF-BY: SHAE

what is the word like "additive" but instead of "things are only added" it
means "things are only corrupted"?

* un-hard-code configuration in the example app
* replace a bunch of partial pattern matches with nice big exhaustive cases
* update some comments about which errors we are losing and where

Co-authored-by: Shae <shae@scannedinavian.com>

* It's a poor way to represent application errors
* It's only intended for interpreting failed pattern matches
* I don't know how to consume it from an Obelisk frontend