[pyos][docs] parameterized, is_udt, and lazy undocumented for user functions #437

The register_new and register_anonymous class methods for different operators have parameters parameterized, is_udt, and lazy that are tested and seem to work but I don't see them documented.

From what I can see in their implementation, this would include

• what each parameter does
• that parameterized, lazy, and both being undefined are mutually exclusive (if: elif: else:)
• return type (in the case that lazy=False)
• any constraints that the function needs to have (these are present implicitly in the descriptions of the operator types but it would be nice to have specific "this function needs to return one of x type" and etc)

Additionally, register_new and register_anonymous are present in all OpBase subclasses, but not in the base class as an abstract method.

part of: pyOpenSci/software-submission#81