449 mad fn

[cdeline]

Update to the calculation of MAD to improve how it handles 2D arrays and dataframes.

• [ ] Code changes are covered by tests
• [x] Code changes have been evaluated for compatibility/integration with GUI
• [x] New functions added to __init__.py
• [x] manualapi.rst is up to date, along with other sphinx docs pages
• [x] Example notebooks are rerun and differences in results scrutinized
• [x] Updated changelog

[cdeline]

Still want to add a pytest for mismatch_fit3

[cdeline]

Fixed by #485