v1.4.0 - feat(Memorize): concise stateful sequence selector etc

Memorize is a stateful tick wrapper, as an alternative to the (admittedly, rather obtuse) Sync implementation, which wraps child nodes directly. Both implementations address the same core problem case; Memorize is simpler and more intuitive, and should be used unless the flexibility provided by Sync is necessary.

Also improves documentation, including a link to the academic paper that this simplified mechanism was modeled after.