Replace DressedType with parameters on all the Types.

[jpivarski]

Making DressedType a new Type object complicates the hierarchy (different structure than the bare type). Each Type has an (unused) parameters, which should instead be used to augment the existing Type objects in an unchanged hierarchy.

The wrapper class (currently the "dress") can become an entry in the parameters named __class__, and this leaves room for a Numba wrapper and higher-array wrapper classes.

The Dress and PyDress classes should go away, but the Parameters and PyParameters stay. All of the existing Types must now be templated on the Parameters type. Its parameters should probably become std::map<std::string, py::object> rather than py::dict so that the parameter names, at least, can be inspected on the C++ side. Because of Numba (#31), all of those Python objects need to be hashable and pickleable, so there's a natural serialization that can be performed on the C++ side (because PyParameters defines the picklization into bytestrings).