* Don't cache hash codes across deserialization.

 Because the hash code cache field gets serialized and deserialized by
 Pickle, previously when you deserialize a cache_hash=True attrs object, the
 hashcode will be the hashcode the object had at serialization-time.
 However, if your object had fields with hash codes which were not
 deterministic between interpreter runs, then on a new interpreter run
 your deserialized object would have a hash code which differs from a
 newly created identical object.

 This commit fixes that by clearing the cache on deserialization. It
 needs to override the __setstate__ method to do so, so this commit
 also forbids using a custom __setstate__ on a cache_hash=True object.

Closes #482 .

* Improve exception type

* Minor tweaks to comments formatting

* Fix test for Python 2.7

* Fix error in comment

* Make nomenclature consistent for slotted/dict classes

* Remove hasattr()

* Improve comments and error message for custom __setstate__ + cache_hash=True

* Drop use of  for test classes for cache hash serialization

* Make changelog note this is a breaking change

* Make exception message point to tracking issue

* Fix test classes for Python 2.7

message is deprecated.

Fixes #483

* Clarify execution order in init

Fixes #461

* Clarify attributes are processed in the order of declaration

* Simple past is good enough

Fixes #466

* Use isolated builds

* try to upgrade all the things

* Try to upgrade only setuptools