Dms-tools2

----------
* Moved `CodonVariantTable` class to its own module, `codonvarianttable`.

-----------
* added `muteffects` data type to ``dms2_logoplot``

* added `highlighted_sites` option to `plot.plotSiteDiffSel`

* added `title` to `siteSubsetGGSeqLogo`

* Improve matching of termini tags when there are mismatches in `dms_tools2.pacbio`

* Some updates to `dms_tools2.minimap2.Mutations` objects.

* Added functionality to `dms_tools2.barcodes` to get identity within barcodes, take consensus of sequences with same barcode, and then use barcoded codon variants to call mutations.

* `pacbio.CCS` handles FASTQ as well as BAM input.

--------
* Require Python 3.6 or greater.

* added `pacbio`, `minimap2`, and `seqnumbering` modules.

* ``import dms_tools2`` now imports all non-optional modules in the package

-------
* Improved appearance of histograms created by `findSigSel`

* Fixed ymin for `dms2_logoplot` with small-valued fracsurvive

--------
* Cleaned up organization of examples and added `Dingens2018` and `Lee2018`.

* Fix setting of `matplotlib` backend, which was causing errors.

* Use loose versions in `sra`.

-------
* Make `diffsel` and `fracsurvive` compatible with `this pandas 0.23 update <https://pandas.pydata.org/pandas-docs/stable/whatsnew.html#assign-accepts-dependent-arguments>`_