Modifed validate_demultiplex_fasta.py to address issues in issue #975
Added script extract_barcodes.py, along with a tutorial. Partially addresses request in #531 regarding barcodes in headers.
Made changes suggested by Greg C.
fixes #1086
updated to create and use a top level rarefied table - fixing bug caught by @jrrideout
Added support for specifying threads/cpu (default 1 per CPU) to address issue #1162. Only affects a subset of the functions for usearch61 OTU picking and chimera checking. Also fixed a non-related order-dependent error in tests/test_pick_otus.py
Made modifications to address problems/suggestions for code
Changed docstrings per Greg's request
Fixed conflict in Changelog.Md
Merge branch 'validate_demultiplex_fasta_dup_ids_list' of github.com:/walterst/qiime into validate_demultiplex_fasta_dup_ids_list
Modified code to address comments
fixed indent
added more informative error message for common issue
made changes to remove consternation-causing passive voice.
Merge branch 'master' of github.com:qiime/qiime into issue-1086

Conflicts:
	qiime/workflow/core_diversity_analyses.py
12_10 -> 13_8, and 1.7.0 -> 1.8.0
fixed conflict in Changelog.md
Modifications to resolve documentation errors

I removed:
	doc/scripts/otu_category_significance.rst

I modified to include ```group_significance.py``` instead of ```otu_category_significance.py```:
	scripts/core_diversity_analyses.rst
	tutorials/open_reference_illumina_processing.rst
fixed up a malformed cell
Fix for conflict in tests/test_format.py