* 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