Minor fixes for smoothening with hann windows

[valhassan]

I intend to make fixes based on the comments indicated in this PR (merged) https://github.com/NRCan/geo-deep-learning/pull/486

• add reference article to function docstring
• remove soft coding and add use_hanning bool as a config parameter

For full reference, refer to this issue: https://github.com/NRCan/geo-deep-learning/issues/485