0.8.0

• Find specifications: collection :find [?e ...], tuple :find [?e ?v], and scalar :find ?e .
• Support for :db/isComponent (issue #3)
• Support for nested maps in transact! (also fixes #38)
• [ BREAKING ] Custom aggregate fns must be called via special syntax (aggregate keyword): (q '[:find (aggregate ?myfn ?e) :in $ ?myfn ...]). Built-in aggregates work as before: (q '[:find (count ?e) ...]
• Return nil from entity when passed nil eid (issue #47)
• Transaction data is now validated, with proper error messages (also fixes #48)