* Initial version of vectorized environments
* Raise an exception in the main process if child process raises an exception
* Add list of exposed functions in vector module
* Use deepcopy instead of np.copy
* Add documentation for vector utils
* Add tests for copy in AsyncVectorEnv
* Add example in documentation for batch_space
* Add cloudpickle dependency in setup.py
* Fix __del__ in VectorEnv
* Check if all observation spaces are equal in AsyncVectorEnv
* Check if all observation spaces are equal in SyncVectorEnv
* Fix spaces non equality in SyncVectorEnv for Python 2
* Handle None parameter in create_empty_array
* Fix check_observation_space with spaces equality
* Raise an exception when operations are out of order in AsyncVectorEnv
* Add version requirement for cloudpickle
* Use a state instead of binary flags in AsyncVectorEnv
* Use numpy.zeros when initializing observations in vectorized environments
* Remove poll from public API in AsyncVectorEnv
* Remove close_extras from VectorEnv
* Add test between AsyncVectorEnv and SyncVectorEnv
* Remove close in check_observation_space
* Add documentation for seed and close
* Refactor exceptions for AsyncVectorEnv
* Close pipes if the environment raises an error
* Add tests for out of order operations
* Change default argument in create_empty_array to np.zeros
* Add get_attr and set_attr methods to VectorEnv
* Improve consistency in SyncVectorEnv
