call evaluation_hooks in Evaluator

[keisuke-nakata]

call evaluation_hooks in {Async,}Evaluator instead of train_agent{,_batch,_async}.

This PR is a preparation for unifying evaluation_hooks to use_tensorboard option.
(Interactions with Tensorboard are called in {Async,}Evaluator.)

I also added support_train_agent{,_batch,_async} attributes to EvaluationHook class in order to clarify that which hooks are eligible for each training function (train_agent_with_evaluation, train_agent_batch_with_evaluation, train_agent_async).

---

NOTE: This PR breaks backward compatibility of EvaluationHook.__call__ API. It no longer has eval_score argument. Use eval_stats['mean'] instead (eval_score is equivalent to it).

[pfn-ci-bot]

Successfully created a job for commit 073f688:

• Dashboard for commit 073f688

[pfn-ci-bot]

Successfully created a job for commit ac05424:

• Dashboard for commit ac05424

[pfn-ci-bot]

Successfully created a job for commit 9bb3e19:

• Dashboard for commit 9bb3e19

[muupan]

I'd like you to clarify the plan behind this PR.

• Are you planning to replace use_tensorboard with another evaluation hook, which is implemented after this PR?
• Are other evaluation hooks also planned? e.g. one for mlflow
• Since the change of the arguments are necessary for those tensorboard and/or mlflow hooks, correct?

[keisuke-nakata]

• Are you planning to replace use_tensorboard with another evaluation hook, which is implemented after this PR?
• Are other evaluation hooks also planned? e.g. one for mlflow

Yes.

• Since the change of the arguments are necessary for those tensorboard and/or mlflow hooks, correct?

I unified arguments of EvaluationHook.__call__ to tensorboard's one.
I believe that arguments required by mlflow are included in these (say, env, agent, evaluator, step, eval_stats, agent_stats, env_stats). If these arguments are not suffice for mlflow, I'd like to add some in later PR.

So, remaining tasks are:

• Implement tensorboard option as an EvaluationHook .
• Implement mlflow option as an EvaluationHook. (And add some arguments if mlflow requires more information)

[pfn-ci-bot]

Successfully created a job for commit 22b7c57:

• Dashboard for commit 22b7c57

[pfn-ci-bot]

Successfully created a job for commit 43c2fd4:

• Dashboard for commit 43c2fd4

[keisuke-nakata]

We decided to break backward compatibility for cleaner API.
EvaluationHook no longer has the argument eval_score, but it has contains general information as eval_stats, agent_stats, env_stats. (eval_score is equivalent to eval_stats['mean']).