adding support for get-else as built-in pred
adding support for get-some and missing? as pred fns
adding support for back-ref in missing? pred
Deleted unused compare-key fn (closes #24)
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