Modifed validate_demultiplex_fasta.py to address issues in issue #975
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
Changed docstrings per Greg's request
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
12_10 -> 13_8, and 1.7.0 -> 1.8.0
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
Added the otu_category_significance.rst file back

Now a pointer to use group_significance.py
Merge pull request #1282 from wdwvt1/group_significance

Looks good to me!!
Merge pull request #1280 from gregcaporaso/issue-1075-take2

added more informative error message for common issue
Merge pull request #1265 from walterst/usearch_remove_multithreading2

Added support for specifying threads/cpu (default 1 per CPU) to address ...
Merge pull request #1213 from walterst/validate_demultiplex_fasta_dup_ids_list

Modifed validate_demultiplex_fasta.py to address issues in issue #975
Merge pull request #1283 from wasade/issue1032

Issue1032
Added sentence about suggested memory for using virtual box and newest reference databases
Add wording to rarefaction plots

A brief wording was added to the rarefaction plots, just like it was
discussed in #1172.

The tests were updated to reflect these changes.
Merge pull request #1286 from ElDeveloper/issue_1172

Add wording to rarefaction plots
Merge pull request #1285 from walterst/vm_doc_memory_update

Added sentence about suggested memory for using virtual box and newest r...