Abtools

AbCorrect
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* Added Unix sort for UID clustering
* Made Unix sort the default method for clustering UIDs. CD-HIT is still available by providing the ``--cdhit-cluster-uids`` option

AbCorrect
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* Add ability to directly parse 'MINIMAL' output format from AbStar
* Consensus/centroid sequence creation is now done in batches, size can be set with the --chunksize option
* Option to parse multiple UIDs, useful when dual barcodes are used.
* Stub out distributed processing on Celery clusters (not thoroughly tested yet)

AbStats
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* Started migration of AbStats to just the Stats module, since it's primarily only used via the API (not as a command line program)

AbCorrect
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Performance improvements
Add ability to directly process JSON files (as opposed to requiring sequences to be in a MongoDB database)

Bug Fixes

Add `requirements.txt` to `MANIFEST.in`