Nasdanika CLI operates on top of picocli.
One of its features is generation of HTML documentation site and support
of extended documentation
(https://docs.nasdanika.org/core/cli/index.html#extended-documentation)

Currently this functionality works with CommandSpec by accessing user
object. To extend it to arguments and options it is necessary to be able
to access underlying fields/methods.

This commit introduces IReflector interface implemented by FieldBinding
and Method Binding.