1. fix many Ostap fit models
2. extend interface for PDF2/PDF3 base classes
3. add several new models, namely PS2dPol(2,3)(Sym)-family - non-factorizeable 2D-models,
based on combination of phase-space functions
4. import cubature C-code from https://github.com/stevengj/cubature
(needed for 2D-integration of models from 3rd item
5. fix many Doxygen problems/errors/warnings