Quantiphy

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- Added new standard SI scale factors (*Q*, *R*, *r*, *q*).
- Subclasses of :class:`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: :func:`as_real`, :func:`as_tuple`, :func:`render`,
:func:`fixed`, and :func:`binary`.
- Fixed rendering of full precision numbers in :meth:`Quantity.fixed()`.
- Added *preferred_units* :class:`Quantity` preference.
- Added “cover” option to *strip_radix* :class:`Quantity` preference.
- Added type hints.

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- Support parametrized unit conversions (such as molarity).
- Allow % to act as a scale factor.
- First argument of scaling functions are now guaranteed to be quantities.
- Added :func:`UnitConversion.fixture` decorator function.
- Added :meth:`UnitConversion.activate` method
(allows overridden converters to be re-activated).

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- Refine the list of currency symbols.
- Allows currency symbols to be given before or after the underlying number.
- Allow :class:`Quantity` subclasses to be used in scaling if they have units.

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- Add support for — as comment character and make it the default.

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- Updated predefined physical constants to CODATA 2018 values.
- Switched to more permissive MIT license.
- Add feet to the available length/distance unit conversions.

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- Allow primary argument of :meth:`Quantity.is_close` and :meth:`Quantity.add`
to be a string.