Fixed super constructor argument order for RefArray<T>
Butterflyplan now has feature to be offset relative to another plan (not
completely yet: it is now implemented as a offset only)
Setter renamed to CrossoversSetter, which is less ambiguous.
UniquePtr now has dereference (with exception) method. Also != nullptr
(compare) and = nullptr (free data and set to null) are implemented.
ZeroPhaseCrossover now creates multiple plans based on the frame size.
Lower frequency crossovers might be skipped (and done with traditional
filtering) to make effective length of filter path fit within one frame.