Create TensorForce PR for manually closing agent/model

[lefnire]

Create a PR to TensorForce adding this commit, which manually removes auto-closing agent/model w/in runner.py so that we can work with the model a bit after training (to test, to use in live-mode, etc) - we'll close manually.

Above commit is insufficient. Will need to change all their code instances currently using runner.py and adding agent.close();model.close() after runner.run(). This is the only commit in my fork required for this project, so getting that into upstream will remove my fork as a dep.

[lefnire]

tensorforce/tensorforce#310