improve predicate lookup performance from .7 ms to .1 ms
improve predicate lookup performance from .7 ms to .1 ms

Fixes #309

activerecord-hackery/ransack,avit/ransack,reinteractive/ransack,roman-franko/ransack,Mario245/ransack,Eric-Guo/ransack,laserlemon/ransack,johan--/ransack,martndemus/ransack,AndrewSwerlick/ransack,mariorcardoso/ransack,outstand/ransack,praktijkindex/ransack,nagyt234/ransack,amboxer21/ransack,guilleva/ransack,vaski/ransack