Non cumulative maximum-curvature completeness

[calum-chamberlain]

• Code cleaned up and making use of some numpy foo for gradients
• Tests catch IncompleteRead errors.

What does this PR do?

Computes maximum curvature completeness on the non-cumulative distribution as it should be done.

Why was it initiated? Any relevant Issues?

377

PR Checklist

• [x] develop base branch selected?
• [x] This PR is not directly related to an existing issue (which has no PR yet).
• [x] All tests still pass. - [ ] Any new features or fixed regressions are be covered via new tests. - [ ] Any new or changed features have are fully documented.
• [x] Significant changes have been added to CHANGES.md. - [ ] First time contributors have added your name to CONTRIBUTORS.md.

[calum-chamberlain]

Network timeouts - there is a good chance that I am pushing GeoNet's FDSN too hard. Tests pass locally, merging.