Sciform

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* Add ``.readthedocs.yaml`` and update documentation
``requirements.txt`` for reproducible documentation builds.

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* Fix a date typo in the changelog for the entry for version ``0.22.0``.

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* **[BREAKING]** Rename ``sfloat`` to ``SciNum`` and ``vufloat`` to
``SciNumUnc``
* **[BREAKING]** ``SciNum`` instances do not support arithmetic
operations the same way ``sfloat`` instances did.
This functionality was removed for two reasons.
First, ``SciNum`` uses ``Decimal`` to store its value instead of
``float`` and configuring ``SciNum`` to behave as a subclass of
``Decimal`` would require added complexity.
Second, A decision has been made to keep the ``sciform`` module
focussed solely on formatting individual numbers or pairs of numbers
for early releases.
Convenience functionality outside of this narrow scope will be
considered at a later time.
* Favor ``Decimal`` methods over ``float`` methods in internal
formatting algorithm code.
* Documentation

* Remove ``float``-based language fom documentation.
* Include a discussion in the documentation about ``Decimal`` versus
``float`` considerations that may be important for users.
* Various minor revisions and edits. Notably a typo in the version
``0.21.0`` changelog entry that reversed the meaning of a sentence
was corrected.
* Add "under construction" message to README.

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* Use ``Decimal`` under the hood for numerical formatting instead of
``float``. ``Decimal`` instances support higher precision than
``float`` and more reliable rounding behavior.
* Update particle data group uncertainty rounding unit tests since edge
cases are now handled property as a result of adopting ``Decimal``.
* Minor cleanup of ``sfloat`` arithmetic functions.

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* Refactor unit tests to use lists and tuples instead of dicts. Literal
dicts allow the possibility for defining the same key (test case) with
different values, only the latest of which will actually be tested.
The refactoring ensures all elements of the test lists will be tested.
* Refactor ``sfloat`` and ``vufloat`` ``__format__()`` functions to call
``format_float()`` and ``format_val_unc()`` directly instead of
creating a ``Formatter`` object first.

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* Support passing ``None`` as a value into ``extra_si_prefixes``,
``extra_iec_prefixes``, or ``extra_parts_per_forms`` to prevent
translation of a certain exponent value. This may be useful for
suppressing ``ppb`` or similar local-dependent "parts per"
translations.
* **[BREAKING]** Change the bracket uncertainty flag in the
`FSML <fsml>`_ from ``'S'`` to ``'()'``.
* When an exponent translation mode is used in combination with Latex
mode, the translated exponent will now be wrapped in a Latex text
mode: e.g. ``\text{Mi}``.
* Link to test cases on examples page.

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