Add map.map.flatMap test.
Add `TransfigureInstances.point`.
Add `join` instance and `identity` method.
Introduce `kind-projector` because "we're all mad here".
Refactor syntax using specialized Unapply classes.

Dedicated to @milessabin, for all his time dedicated on kindely shaping types for the rest of us.
Extract `TransfigureTo`.
Add `UnapplyS1` instance for `point`.
Add `UnapplyS1` instance for `traverse_join`.
Reformat `TransfigureTo` instances definition.
Introduce recursive `map` with instances for `UnapplyS1`.