implementation for "unhashable" is wrong

[wbolster]

The implementation to make a class unhashable which has been added in #184 is wrong. See commit daa213d for the changes.

The python data model docs at
https://docs.python.org/3/reference/datamodel.html#object.__hash__ state:

A class that overrides __eq__() and does not define __hash__() will have its __hash__() implicitly set to None. When the __hash__() method of a class is None, instances of the class will raise an appropriate TypeError when a program attempts to retrieve their hash value, and will also be correctly identified as unhashable when checking isinstance(obj, collections.Hashable).

Instead of raising a TypeError from __hash__(), the method should not be present at all, and a __hash__ = None should be in its place, like this:

class SomeClass(...):
    __hash__ = None

    def __eq__(self, other):
        ...

[lxyu]

should be resolved in 9e5a863