split functions into import/export of components

introduced new bug:
postgres2datomic.core=> (table-to-edn "mdl_user" :pg-spec (get-pg-spec) :limit 10)
IllegalArgumentException No implementation of method: :make-writer of protocol: #'clojure.java.io/IOFactory found for class: nil  clojure.core/-cache-protocol-fn (core_deftype.clj:541)