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.p