simplify the Datomic query parser

 - the original code was copied from Datomisca, this cuts it down to a simplified form that is suited for the purpose of Autosource
 - queries must be of the form [:find ?e :where …] or {:find [?e] :where […]}
 - upgrade to the latest Datomic version
Merge pull request #29 from dwhjames/topic/datomisca-query-parser

simplify the Datomic query parser