* code refactor; remove unused kwargs; add reward_normalization for dqn
* bugfix for __setitem__ with torch.Tensor; add Batch.condense
* minor fix
* support cat with empty Batch
* remove the dependency of is_empty on len; specify the semantic of empty Batch by test cases
* support stack with empty Batch
* remove condense
* refactor code to reflect the shared / partial / reserved categories of keys
* add is_empty(recursive=False)
* doc fix
* docfix and bugfix for _is_batch_set
* add doc for key reservation
* bugfix for algebra operators
* fix cat with lens hint
* code refactor
* bugfix for storing None
* use ValueError instead of exception
* hide lens away from users
* add comment for __cat
* move the computation of the initial value of lens in cat_ itself.
* change the place of doc string
* doc fix for Batch doc string
* change recursive to recurse
* doc string fix
* minor fix for batch doc
* Add auto alpha tuning and exploration noise for sac.
Add class BaseNoise and GaussianNoise for the concept of exploration noise.
Add new test for sac tested in MountainCarContinuous-v0,
which should benefits from the two above new feature.
* add exploration noise to collector, fix example to adapt modification
* fix#98
* enable off-policy to update multiple times in one step. (#99)
* add_pybullet_ens_test
test on pybullet envs
modify some log config
* delete DS_Store file
* add pybullet_envs test
add HalfCheetahBulletEnv-v0 test
modify log config
* fix pep 8 errors
* add pybullet to dev
* delete a line
* by pass F401
* add log_interval to onpolicy_trainer
* add comments
* Update halfcheetahBullet_v0_sac.py
* update atari.py
* fix setup.py
pass the pytest
* fix setup.py
pass the pytest
* add args "render"
* change the tensorboard writter
* change the tensorboard writter
* change device, render, tensorboard log location
* change device, render, tensorboard log location
* remove some wrong local files
* fix some tab mistakes and the envs name in continuous/test_xx.py
* add examples and point robot maze environment
* fix some bugs during testing examples
* add dqn network and fix some args
* change back the tensorboard writter's frequency to ensure ppo and a2c can write things normally
* add a warning to collector
* rm some unrelated files
* reformat
* fix a bug in test_dqn due to the model wrong selection
