* New primary interface #call makes specs and implementations much
easier
* We had #each mostly for historical reasons that are not relevant
anymore
* Mutation covers the Mutant::Matcher namespace
* Before Mutant::Expression was not marshallable resulting in the need
to build "partial" result objects from killforks.
* Fixes an adjacent bug in spec selection
* Do not mix concerns of domain with building an object graph concerning
the domains execution environment
* Removes the amount of clutter in Env (mostly a cleanup for tracing
where Env will grow a bit)