Write documentation for CDigitalSet. CDigitalSet is now a model of CPointPredicate. Update models of CDigitalSet to be models of CPointPredicate.
Update models of CPointPredicate in doc.
Add documentation for module digital sets. Update DigitalSetDomain and SetPredicate.
Update kernel concepts.
Merge branch 'master' of github.com:DGtal-team/DGtal into Fix435
Removes SetPredicate from all files, tests and examples.
Correct bug in DomainAdjacency. Correct long-standing bug in Expander due to mix proxy predicate and set.
Update doc in moduleDigitalSets accordingly.
Merge pull request #558 from JacquesOlivierLachaud/Fix435

Fix435 and Fix522