Changes serialization mechanism of closures from serialize-fn to regular java serialization. With this change, all functions used in Spark jobs must be compiled (aot).
Merge remote-tracking branch 'dajac/flambo/serialization' into serialization

* dajac/flambo/serialization:
  Changes serialization mechanism of closures from serialize-fn to regular java serialization. With this change, all functions used in Spark jobs must be compiled (aot).

Conflicts:
	project.clj
	src/clojure/flambo/api.clj
	src/clojure/flambo/function.clj
	test/flambo/api_test.clj
* fixed broken test (basically due to serialization of function)
* code cleanup