added a script to calculate the moment magnitude from the output of QM

[tmgreenfield1101]

What is the purpose of this Pull Request?

To add functionality to calculate moment magnitudes

Relevant Issues

none

Test cases

This doesn't alter the core code, but instead adds a new folder scripts where scripts and functionality can be easily added

• [ 1] All examples run without any new warnings
• [ 1] test_benchmarks.py reports all example tests pass

System details

macosx

Final checklist

• [1 ] develop base branch selected?
• [ 1] All tests still pass.
• [1 ] Any new features or fixed regressions are covered by new tests.
• [1 ] Any new or changed features are fully documented.
• [1 ] Significant changes have been added to CHANGES.md.
• [1 ] First time contributors have added your name to CONTRIBUTORS.md.

[hemmelig]

I have changed the PR to point at the master branch, rather than develop (which is out of sync right now).