cosmetic refactoring of StarterProcess variants of ToChildStart

Moved helper functions to where clauses. See the discussion on PR #77.
move exported types from C.D.P.P.Supervisor to .Types

This is in preparation for some changes to the handling of the
StarterProcess variants of ToChildStart. See discussion on PR #77.
rm Control.Distributed.Process.Platform.Supervisor.Types from exposed-modules
refactor Supervisor ToChildStart instances

Cosmetic refactoring of StarterProcess variants of ToChildStart.
Refactor/Relocate Supervisor Types