Azadkia-Chatterjee coefficient

[kahaaga]

Implements #380.

The docs are here.

This PR contains

• The AzadkiaChatterjeeCoefficient struct, which dispatches to association with either two or three input datasets (corresponding to pairwise or conditional association) + tests.
• Implementations for AzadkiaChatterjeeCoefficient for both SurrogateAssociationTest (pairwise and conditional) and LocalPermutationTest (conditional) + tests.
• A listing for AzadkiaChatterjeeCoefficient in the documentation pages.
• Cross references in AssociationMeasure and AssociationMeasureEstimator docstrings.
• Many runnable documentation examples that are cross-referenced everywhere necessary (example 1, example 2).