now recognizing the api's total rows header
less assignment in if stmt = better code
added total rows getter
make it possible to handle 0 total rows
moved total row count to Collection
added test for get/set total rows
added test for total rows extraction from api headers
now using null to denote "no total rows"
Merge pull request #29 from easybiblabs/topics/support-total-rows

expose total rows of the set represented by a Collection (from API response header)