Compatibility with StateSpaceSets v2

This PR: - Adds various fixes/tweaks for compatibility with StateSpaceSets.jl v2. - Adds various fixes/tweaks for compatibility with ComplexityMeasures v3.X, which depended on the above point. - Improved documentation strings for a few mutual info estimators. - Increments minor version to 4.3 and adds a corresponding changelog entry. - Adds more tests for `OCE` The user-facing API is not changed in any way - only internals. Closes #389.