Change progenitor_binding to simpler progenitor

See #delete_if in lib/iterable_array/iterators.rb... previously used
Binding#eval because of misunderstanding of how object references work
(I think I thought that they duplicated the object...silly-willy). Now I
directly reference the outermost IterableArray object as `@progenitor`.

Likely could be simplified further (see #new_with_progenitor and

Covered by two tests (which still pass).
Increment minor version number