doc: cluster documentation cleanup and corrections

Fixed some incomprehensible wording ("event assigned to..."?), removed
undocumented and unnecessary process properties from example, corrected
the docs on the default for the exec setting, described when workers are
removed from cluster.workers, and described addressType, which was
documented as existing, but not what values it might have.
doc: cluster documentation cleanup of setupMaster

Remove redundant documentation, and spell out more clearly the
limitations of setupMaster.
doc: cluster disconnect and master/child differences

- describe disconnect in sufficient detail that why a child does or does
  not exit can be understood
- clarify which cluster functions and events are available on process or
  just on the worker, as well as which are not available in children,
- don't describe events as the same, when they have receive different
  arguments
- fix misleading disconnect example: since disconnect already calls
  close on all servers, doing it again in the example is a no-op,
  not the "force close" it was claimed to be
- document the error event, not catching it will kill your node