allure.environment is missing in allure.py

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#### I'm submitting a ...
- [x] bug report
- [ ] feature request
- [ ] support request => Please do not submit support request here, see note at the top of this template.

#### What is the current behavior?
Based on documentation [here](https://github.com/allure-framework/allure-pytest) to apply some environment configurations we should use allure.environment(report='Allure report', browser=u'Я.Браузер') syntax. But in allure.py environment is missing. Before we have to use some environment.properties file in report folder to apply variables to the report. New functionality is missing.
Content of allure.py:
```
from allure_commons._allure import label
from allure_commons._allure import severity
from allure_commons._allure import tag
from allure_commons._allure import epic, feature, story
from allure_commons._allure import link
from allure_commons._allure import issue, testcase
from allure_commons._allure import Dynamic as dynamic
from allure_commons._allure import step
from allure_commons._allure import attach
from allure_commons.types import Severity as severity_level
from allure_commons.types import AttachmentType as attachment_type

__all__ = [
'label',
'severity',
'tag',
'epic'
'feature',
'story',

'link',
'issue',
'testcase',

'step'

'dynamic'

'severity_level',

'attach',
'attachment_type'
]

```

#### If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

#### What is the expected behavior?

#### What is the motivation / use case for changing the behavior?

#### Please tell us about your environment:

- Allure version: 2.2.1
- Test framework: pytest@3.5
- Allure adaptor: allure-pytest@2.1.0b1

#### Other information

[//]: # (
. e.g. detailed explanation, stacktraces, related issues, suggestions
. how to fix, links for us to have more context, eg. Stackoverflow, Gitter etc
)

Bắt đầu với allure.py và so sánh API được export của nó với tài liệu allure-pytest được liên kết trong issue, tập trung vào cú pháp allure.environment được tài liệu hóa. Kiểm tra phần thảo luận hiện có của issue để nắm bối cảnh và xác định API công khai được mong đợi; được xem là hoàn tất khi cấu hình môi trường được tài liệu hóa có thể được sử dụng thông qua allure.py và hoạt động như mô tả.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.