AssertionError vs Exception

Currently Allure fails only on AssertionError and all Exception is treated as Broken.
This is a good feature but pytest reports them as Fail. This causes a bit of confusion on the report status.

An intermediate approach can be to allow for option on what constitutes a fail.
A suggestion is to provide an API where one can register baseclasses that can be as failures. This provides for better control to use with infrastructures that can have some common analysis to look for additional failures.

```
def get_status(exception):
if exception:
if isinstance(exception, AssertionError) or isinstance(exception, pytest.fail.Exception):
return Status.FAILED
elif isinstance(exception, pytest.skip.Exception):
return Status.SKIPPED
return Status.BROKEN
else:
return Status.PASSED
```

=> Something like...

```
def get_status(exception):
if exception:
for base_class in allure.FailExceptionList:
if isinstance(exception, base_class):
return Status.FAILED
elif isinstance(exception, pytest.skip.Exception):
return Status.SKIPPED
return Status.BROKEN
else:
return Status.PASSED
```

この issue では実装ファイルもテストも指定されていません。まず、get_status とその pytest 統合によって表される、既存の例外からステータスへの経路を特定します。完了条件は、failed、skipped、broken、passed のステータス処理を維持しながら、設定可能な例外基底クラスを許可することです。

索引モデルが issue の本文から書いたものです。