Add a whitelist for short numbers and fix API
Add a whitelist for short numbers and fix API

This implements separate functions compact() and format() and fixes the
doctests. This also implements a whitelist of registered short numbers
to avoid accidentally validating just any number.

holvi/python-stdnum,arthurdejong/python-stdnum,holvi/python-stdnum,arthurdejong/python-stdnum,arthurdejong/python-stdnum,t0mk/python-stdnum,dchoruzy/python-stdnum,holvi/python-stdnum