support :if option for conditional indexing
run all specs when everything filtered
support :unless option for conditional indexing
Merge pull request #10 from zapnap/index_conditional

Support :if and :unless options for conditional indexing
Add :if/:unless options to the README. Ref #8
Add notes about method aliases
Bump to 1.7.1 (fix #8)
support STI subclasses (via parent index)
Merge pull request #11 from zapnap/support_subclasses

support single table inheritance / subclasses (via parent index)