Flexible Custom MLP Policies + bug fixes
- added support for storing model in file like object. (thanks to @erniejunior)
- fixed wrong image detection when using tensorboard logging with DQN
- fixed bug in ppo2 when passing non callable lr after loading
- fixed tensorboard logging in ppo2 when nminibatches=1
- added early stoppping via callback return value (@erniejunior)
- added more flexible custom mlp policies (@erniejunior)