Comparators and projections

Most sorting algorithms in cpp-sort accept comparison and/or projection parameters. The library therefore considers these kinds of functions to be first-class citizens too and provides dedicated comparators, projections and tools to combine them and to solve common related problems.

All the functions and classes in cpp-sort that take comparison or projection functions as parameters expect Callable parameters, which correspond to anything that can be used as the first parameter of std::invoke. This allows to pass entities such as pointers to members or pointer to member functions to the sorting algorithms; it should work out-of-the-box without any wrapping needed on the user side.