MAINT: Update emperor requirement

Previously was pointing to 0.9.3 and 0.9.4-dev, now states it needs
a version greater than 0.9.5 and lesser than 1.0.0.

I also updated a link for scikit-bio.

Related to #1716
Merge pull request #1720 from ElDeveloper/emperor-0.9.5

MAINT: Update emperor requirement
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
MAINT: updated biom requirement, partial fix for #1716
Merge pull request #1727 from gregcaporaso/issue-1716

updated biom requirement in prep for QIIME 1.9.0