Version 1.0.1

[iantbeck]

Add support for gradient calculation with neural network models and minor bugs

[sgoodlett]

Does this PR fix the issues seen with issues #31 and #22? I believe in those that PES-Learn was installed with conda but within the inner workings of PES-Learn, the PIPs library is somehow not found. If not, it should be an easy fix.

[iantbeck]

The PR did not initially fix issues #31 and #22, but it should now.
The problem was that when conda (or a Python venv) created the site-package, the text files located in peslearn/lib/ were not being copied since they were not being used directly. To solve this I changed all 'output' in each dir within peslearn/lib/ to be output.py and created __init__.py files for each directory. The workaround mentioned in issues #31 and #22 allowed python to find these files directly, but this should fix that so the manual setting of PYTHONPATH is no longer necessary.

It does seem somehow more CI issues have now emerged, fixes for that to come soon.