Mirror / Mirrored state

Mirrored state: foldkit-mirror

Some local state should outlive the page or be linkable: the filter and page a list shows, the search text, a collapsed sidebar, a half-written draft. Two stores fit: the URL for what a link should carry, and a key-value store for what a device should remember. foldkit-mirror keeps a slice of the Model in step with either. The Model stays the only truth; the store is a mirror.