Missing `__version__` attribute

### Which version of the SDK was used? Please provide the output of `pip freeze`.

```
...
azure-common==1.1.16
azure-storage-blob==1.4.0
azure-storage-common==1.4.0
azure-storage-file==1.4.0
azure-storage-queue==1.4.0
...
```

### What problem was encountered?

I cannot retrieve the module version because __version__ is missing in both `azure` and `azure.storage.blob` (see below). I thought that was a pretty standard way to do it see [PEP 396](https://www.python.org/dev/peps/pep-0396/) and [this issue](https://github.com/explosion/spaCy/issues/608)

```
>>> import azure
>>> azure.__version__
Traceback (most recent call last):
File "", line 1, in
AttributeError: module 'azure' has no attribute '__version__'
```