doc: child_process corrections and cleanups

- Make explicit that .disconnected is set before the disconnect event,
  and it is not allowed to send messages after calling .disconnect(),
  even while waiting for a delayed disconect event.
- Remove obsolete claim that explicit exit is required
- Describe silent: in the options for fork()
- Describe .connected as the property it is, not just as an aside in
  the disconnect() method
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
doc: cluster doc comments addressed
doc: cluster suicide described better

Suicide is important, and a bit unintuitive (process.exit() is not
suicide?). Also, use worker consistently throughout, instead of child.
doc: cluster, limit line lengths to 80