updates to ChangeLog for 1.6.0
renaming to display on GitHub page
adding md formatting for 1.6.0 changes
incremental updates as I work through commit history
more incremental updates after working through commit logs.
fix for issue #579
Merge pull request #580 from gregcaporaso/issue-579

fix for issue #579
added updated dependency versions
clarified note in previous commit
fixed error in PyCogent version number
Merge pull request #578 from gregcaporaso/1.6.0-ChangeLog

ChangeLog updated for QIIME 1.6.0
updated __version__ and __status__ strings and references to the version number.
Merge pull request #581 from gregcaporaso/160-release

updated __version__ and __status__ strings and references to the version...
Updated version info for 1.6.0 release. Modified upgrade doc to be more concise and not duplicate other documentation.
updated handling of nan to address test failure
Updated description to address Greg's comment.
documentation improvement
Merge pull request #584 from jrrideout/1.6.0_release_prep

Updated version info for 1.6.0 release. 
Added .gitattributes.
fixed typo