v2.19

• Added new standard SI scale factors (Q, R, r, q).
• Subclasses of Quantity with units now convert values to the desired units rather than allowing the units of the class to be overridden by those of the value.
• Added scale factor conversion.
• Added quantity functions: as_real, as_tuple, render, fixed, and binary.
• Fixed rendering of full precision numbers in Quantity.fixed().
• Added preferred_units Quantity preference.
• Added “cover” option to strip_radix Quantity preference.
• Added type hints.