Document new :load-ns option to deftype/defrecord introduced by CLJ-1208

was applied in 1.8 alphas and contains a new :load-ns option for defrecord and deftype but did not document that in the docstring.

This ticket adds documentation for that feature to the docstring.

Additionally, text should be added to http://clojure.org/datatypes.

Patch: clj-1823-2.patch