Make #lang syndicate module-begin gather boot actions into a
syndicate-main submodule, and for each such module, add a main
submodule that calls run-ground with the syndicate-main boot actions.
This lets us write syndicate *libraries* that comprise both
data-structures, functions, and Syndicate services.
This is Syndicate/Racket v2, modeled more closely after Syndicate/js.
Facets and Endpoints are now contained within a single actor, unlike
Syndicate/Racket v1, where a linkage protocol between multiple actors
was used. The approach to actor and facet state has been revised as a
consequence.
Almost all the examples using syndicate/actor have been updated.