Read numdb files in context manager
Read numdb files in context manager

This ensures that the file is explicitly closed in the function to avoid
"unclosed file" warnings.

See: https://github.com/arthurdejong/python-stdnum/issues/33

holvi/python-stdnum,arthurdejong/python-stdnum,arthurdejong/python-stdnum,holvi/python-stdnum,holvi/python-stdnum,arthurdejong/python-stdnum