Dms-variants

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Added
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- Gaps (``-``) are now valid characters

Changed
+++++++
- formatted code with ``black`` and added to Travis tests.

Changed
+++++++
- Increased width of docs

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Added
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- Added ``inverse_simpson_index``

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Added
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- Added ``allowed_aa_muts`` parameter to ``simulate_CodonVariantTable``.

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Changed
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- Require Python >= 3.8
- Moved `BinaryMap` to its own package at https://github.com/jbloomlab/binarymap

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Fixed
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- Require Python >= 3.7
- Increase ``pandas`` version requirement
- Fix plotting bugs with ``plotnine`` 0.8.0 by remove unused categories in Categoricals

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Fixed
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- Fixed bug in ``extra_cols`` to ``CodonVariantTable.from_variant_count_df`` implementation.