itkwidgets.__version__ not available

[tbirdso]

Expected behavior

>>> import itkwidgets
>>> print(itkwidgets.__version__)
1.0a33

Observed behavior

>>> import itkwidgets
>>> print(itkwidgets.__version__)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-58-5993d2d9bb44> in <module>
----> 1 itkwidgets.__version__

AttributeError: module 'itkwidgets' has no attribute '__version__'

cc @thewtex @bnmajor