Xlcalculator

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- Nothing changed yet.

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- Added support for Python 3.10, dropped 3.8.

- Upgraded requirements.txt to latest versions.

* `yearfrac==0.4.4` was incompatible with latest setuptools.

* `openpyxl` had API changes that were addressed and tests fixed.

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- Make sure that decimal rounding is only set in context and not system wide.

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- Fixed cross-sheet references.

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- Pass ``ignore_hidden`` from ``read_and_parse_archive()`` to
``parse_archive()``

- Add Excel tests for ``IF()``.

- Add ``NOT()`` function.

- Implemented ``BIN2OCT()``, ``BIN2DEC()``, ``BIN2HEX()``, ``OCT2BIN()``,
``OCT2DEC()``, ``OCT2HEX()``, ``DEC2BIN()``, ``DEC2OCT()``, ``DEC2HEX()``,
``HEX2BIN()``, ``HEX2OCT()``, ``HEX2DEC()``.

- Drop Python 3.7 support.

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- Add support for cross-sheet references.

- Make ``*IF()`` functions case insensitive to properly adhere to Excel specs.

- Support for Python 3.9.