* sync internal changes. Make ddpg work with vecenvs
* B -> nenvs for consistency with other algos, small cleanups
* eval_done[d]==True -> eval_done[d]
* flake8 and numpy.random.random_integers deprecation warning
* store session at policy creation time
* coexistence tests
* fix a typo
* autopep8
* ... and flake8
* updated todo links in test_serialization