add roc curve

[nicholasloveday]

closes #46

[nicholasloveday]

This is still work in progress.
TODO

• Finish roc_curve_data metric unit tests
• Raise error if values outside [0,1] in ROC
• Update dim handling in ROC
• Update ROC docstring
• Jupyter notebook

[nicholasloveday]

It also may need to be updated if #71 is merged in first.

[nicholasloveday]

Since this is a large pull request, here is the suggested order that I think would be good to tackle the code review.

1. Start with the tutorial notebook to get an overview
2. Review the updated processing code
3. Review the categorical binary metrics
4. Review the ROC implementation.

[aidanjgriffiths]

Hey @nicholasloveday, there has been some changes to the test directory structure changes in develop which will resolve in some conflicts from #77. Theres a couple of suggetions in this review but its best if I do a more in depth review once the test suite conflicts are sorted out.

[nicholasloveday]

Thanks @aidanjgriffiths - I've rebased and resolved conflicts. Ready for you to have another look at it.

[aidanjgriffiths]

Looks good @nicholasloveday!

[tennlee]

I have left a small number of comments but they require addressing. Thanks for this significant contribution.

[nicholasloveday]

Thanks @tennlee, I've made those changes.