Dms-tools2

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* fix bug in `diffsel.tidyToWide` such that sites with matching values (i.e. all 0 values) are not dropped during de-duplication.

* added `utils.codonEvolAccessibility` function

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* fix bug in stringency re-scaling by ``dms2_logoplot``

* fix bug in axis scaling in `plot.plotCumulMutCounts`

* added `Haddox2018` and `Doud2018` examples and doc links

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* added `contour` option to `plot.plotCorrMatrix`

* added `white_bg` to `plot.plotSiteDiffSel`

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* added `plot.findSigSel`

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* added `--bclen2` option to ``dms2_bcsubamp``

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* added `protstruct` module for operations related to protein structurs

* added `neutcurve` module to fit neutralization curves

* updated required versions of some dependencies