Consider adding decorators to work with generators

After think a lot about #355 it will be great to provide the same mechanisms we have to "normal" functions to generators!
It is not uncommon to see generators in many Python code, we use it when reading a file, iterating over Query objects and so on!

Today is impossible to work with generators using our current set of decorators like `@safe`:
```python
>>> from typing import Generator
>>> from returns.result import safe
>>>
>>> def numbers() -> Generator[int, None, None]:
... for x in range(2):
... yield x
...
>>> for number in numbers():
... print(number)
...
0
1
>>> for number in safe(numbers)():
... print(number)
...
Traceback (most recent call last):
File "", line 1, in
TypeError: '_Success' object is not iterable
```

Expected behavior:
```python
>>> from returns.result import safe_iter
>>>
>>> for number in safe_iter(numbers)():
... print(number)
...

```