* set default return value of functional types as _mock_return_value
* added test of wrapping child attributes
* added backward compatibility with explicit return
* added docs on the order of precedence
* added test to check default return_value
Mock objects which are not unsafe will now raise an AttributeError when accessing an
attribute that matches the name of an assertion but without the prefix `assert_`, e.g. accessing `called_once` instead of `assert_called_once`.
This is in addition to this already happening for accessing attributes with prefixes assert, assret, asert, aseert, and assrt.