Add TODO with some ideas we had
Get rid of ages-old TODO
Add a read-layer option to ruminating layers.

By default ruminate will "delegate" reads to its input layer, but now
it is possible to delegate to one of the output layers instead.
When id is nil, typed-layer skips its type check
Clean up update-in-node in masai layers to use dispatch-update
Let read-wrapper's args and keyseq depend on the current layer
WIP on resettable layer