Spec actors.lisp, as necessary for scalpl

Background

See https://github.com/adlai/scalpl/blob/a8abce4/actor.lisp for singular PoC, and http://archive.adaic.com/standards/83rat/html/ratl-13.html for precedent.

Improvements to native resource management

Localization of processes

Granularity of context switches

Introspection and debuggability