awickert/GRLP: v1.4.0: PyPI tools + v1.3.1 updates

• Added helper shell scripts to publish code with PyPI: goal to keep these in synch from this point onwards.

In addition, includes the v1.3.1 updates, which on further review add functionality in a way that is more in line with a "minor" update than a "patch" update. Copy/pasting these here:

• Compute width and depth with the aid of grain-size information (optional)
• Update some examples (Python 3; core code updates)
• Directionality to S0
• Test variable gravel inputs and attrition in test_uplift_equals_qs.py