Remove register_class from API. (#550)

* Perform ray.register_class under the hood.

* Fix bug.

* Release worker lock when waiting for imports to arrive in get.

* Remove calls to register_class from examples and tests.

* Clear serialization state between tests.

* Fix bug and add test for multiple custom classes with same name.

* Fix failure test.

* Fix linting and cleanups to python code.

* Fixes to documentation.

* Implement recursion depth for recursively registering classes.

* Fix linting.

* Push warning to user if waiting for class for too long.

* Fix typos.

* Don't export FunctionToRun if pickling the function fails.

* Don't broadcast class definition when pickling class.

python/ray/experimental/array/distributed/core.py

@@ -72,10 +72,6 @@ class DistArray(object):
     return a[sliced]
 
 
-# Register the DistArray class with Ray so that it knows how to serialize it.
-ray.register_class(DistArray)
-
-
 @ray.remote
 def assemble(a):
   return a.assemble()