Basework for changes to otu_cat_sig so that you can sweep through directories, and collate or not collate the results
script can now accepted an input dir or input file, if input dir, the user has the option to collate the results into a single file, or produce a results file for every table in the passed directory. Specifying an output directory is now a required paramater to avoid confusion.
Changed @ElDeveloper's style suggestions
Added new usage example for input directory
Removed unnecessary imports at beginning of script
Updated ChangeLog.md to reflect additions to otu_category_significance for @gregcaporaso
Merge branch 'master' of git://github.com/qiime/qiime into otu_category_significance

Conflicts:
	ChangeLog.md
Merge pull request #782 from lkursell/otu_category_significance

Otu category significance