Micca

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* VSEARCH updated to version 2.7.1;
* Denoising protocol added to the otu command for Illumina reads (UNOISE);
* -S/--chim-abskew option added to micca otu command;
* Documentation updated;
* multithread option added to the mergepairs command.

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* Definitely fix the "new-line error" in classify;
* Fix bar plots in "stats".

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* Fix the "new-line error" in classify.

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* swarm updated to version 2.1.12;
* Now the mergepairs command allows merging staggered reads by default.
With the new option ``-n/--nostagger`` the command produces the same
results of the previous versions (<=1.5);
* classify and tabletotax commands now strip the ``D_X__`` prefix from the Silva
taxonomy files;
* Documentation updated;
* Fix: remove duplicate file closing in micca.api.merge().

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* Now the NAST algorithm trims candidate sequences to that which is bound by the
beginning and end points of the alignment span; with the new option
``--nast-notrim`` in ``micca msa`` produces the same results of the previous
version (<=1.4.0);
* Y-scale in ``micca tablebar`` when ``--raw`` fixed;
* "text file busy error" in ``micca msa`` (nast) fixed;
* pandas deprecation warnings fixed;
* documentation updated.

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* No-filter option added to ``micca.api.msa.nast()`` (do not remove positions
which are gaps in every sequenceces) and to the ``msa`` command
(``--nast-nofilter`` option);
* documentation improved.