Fixes issue #95

The way that we can provide `Sequence` objects to work with `_quantity` parameter is by moving it from recipe's definition to `Mommy._make`. This happens because the quantity is evaluated only inside the `make` function, which is called by `make_recipe`. So, the recipe itself does not even know that there is this option of creating more than one object.

This approach leads us to the discussion of issue #81. Maybe using the proposed idea of this pull request, we can achieve a nice API and make that new feature real.