Add a curves module and a StandardFeatures transformer to extract features from them

[gtauzin]

Reference issues/PRs

Types of changes

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

Description

• Adds a curves module to process and extract features from Betti, Landscape and Silhouette
• Adds a StandardFeature transformer that can return a variety of functions on those curves as features
• Make PersistentLandscape return a 3D array, i.e. a multicurve that can be processed by the curves transformers too.

Screenshots (if appropriate)

Any other comments?

Checklist

• [x] I have read the guidelines for contributing.
• [x] My code follows the code style of this project. I used flake8 to check my Python changes.
• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.
• [ ] All new and existing tests passed. I used pytest to check this on Python tests.

[CLAassistant]

All committers have signed the CLA.

[gtauzin]

Just requiring you review for the curves.StandardFeature transformer.

[gtauzin]

@ulupo @wreise Ready for a full review!

[gtauzin]

Note to self add module to main init and to documentation.

[gtauzin]

@ulupo I know you want to suggest to keep PersistenceLandascape and flatten all nd arrays into 2darrays here xD

[ulupo]

Note to self: Check PersistenceLandscape documentation again.

[gtauzin]

@ulupo I have an idea to greatly simplify hyperparams validation. Once the agreed changes are made, I will give it a try!

[ulupo]

@gtauzin ok cool! I'll give you a signal when I'm done with the changes.