Removed examples directory.

* Will be replaced with the unit tests and documentation.
Added sphinx build and venvs to gitignore.
Added Metaclass test.

* It tests to make sure unrelated attributes are left along.
* Weird stuff was happening because of the use of __slots__ which has
  side effects I'm not aware of. Either way, I'm abusing that feature
  of Python and I should handle unspecified fields differently.