Yipuz.more robust loss

[YipuZhao]

Motivation and Context

Adding two robust loss implementations to extend the types of inner optimization in theseus:

• graduated non-convexity (GNC) loss, based on GemanMcClure
• Hinge loss

How Has This Been Tested

Hinge loss is added to existing robust loss test script; GNC loss is covered by a new test script adapted upon existing robust loss unit test.

Types of changes

• [ ] Docs change / refactoring / dependency upgrade
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have completed my CLA (see CONTRIBUTING)
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[YipuZhao]

Thanks a lot for this contribution @YipuZhao! Mostly code structure changes for now (haven't checked the math).

Can you also add a comment with a reference link to where these losses are described (like a paper or book citation/link).

Thanks for the review! I revised things per your comment, but for now kind of stucked at precommit hook (comment above) and curious about your take. Thanks for any suggestions!

[YipuZhao]

Thanks for adding this @YipuZhao!

Thanks for the comments! Revised and rebased :)