formatdown 0.2.0

new features

• New format_nucl() formats chemical isotopes in nuclear notation.
• formatdown_options() gains the Z and warn arguments used by format_nucl().

minor improvements and fixes

• format_numbers(0, format = "sci") now correctly yields a zero without power-of-ten notation. Likewise for format = "engr" (#10).
• In formatdown_options(), multiply_mark can now be set to "\\cdot" (center dot), often used when decimal_mark is a comma.