Dms-variants

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Fixed
++++++

- Bug fix in ``filter_by_subs_observed``.

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Added
+++++
- ``CodonVariantTable.escape_scores`` now computes score type ``frac_escape``.

- Added ``filter_by_subs_observed``.

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Changed
++++++++
- ``CodonVariantTable.escape_scores`` now requires specification of score type, and implements a new score type of log fraction escape. The output of this method is also slightly changed.

Fixed
+++++
- Bug in calculation of variance in ``CodonVariantTable.escape_scores``.

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Fixed
+++++
- Fixed bug in ``CodonVariantTable.escape_scores`` that sometimes gives null escape scores.

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Added
+++++
- Added ``CodonVariantTable.escape_scores``

- Added ``CodonVariantTable.add_frac_counts``

- Added ``CodonVariantTable.plotCountsPerVariant``

Fixed
++++++
- ``CodonVariantTable.classifyVariants`` requires instructions on how to handle non-primary targets.

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Added
+++++
- Added capability of having other "reference" targets in a ``CodonVariantTable``.

Fixed
+++++
- ``simulate.rand_seq`` generates unique sequences.