MAINT: removed dependencies that are not directly imported in QIIME
MAINT: added note on this change, fixes #1719
MAINT: clarified text
MAINT: fixed typo
MAINT: removed changelog lines regarding changes that only occurred in the 1.8.0-dev cycle (i.e., never made it to a relase)
Merge pull request #1722 from gregcaporaso/issue-1719

update dependencies in setup.py