- update to 0.10.0:
* AtomMeta: create the class only once all members have been
customized
This allows to use ``__init_subclass__`` since previously the
``__atom_members__`` was not set when ``__init_subclass__``
was called
* illustrate the use of ``__init_subclass__`` to customize
pickling
* refactor the metaclass to make it easier to reason about
* add a ``DefaultDict`` member which enforce the value to be a
dictionary and use a factory for missing keys. The factory
is set at the member level and a normal dict can be provided
as value. When possible the factory is deduced from the member
used for validation.
* infer the use of ``DefaultDict`` from a
``collections.defaultdict`` annotation