adding support for :db.fn/cas in transactions
modifying exception message on :db.fn/cas and adding support/test for cas against multival attr.
:db.fn/cas phrasing tuned (closes #20)
Version bump
Added `ground` query fn, fixed query predicate/fn calls without free vars (closes #25)
Retract incoming entity references on `:db.fn/retractEntity` (closes #18)
Support for reverse relation name when transacting entity as a map