Changing `Atoms` class constructor logic.
Changing `Atoms` class constructor logic.

Changing `Atoms` class constructor to be more robust
against an `atoms` argument that is not a list.

Also casts each atom in the list of atoms to the
respective expected type for the given container
class.

androomerrill/scikit-nano,scikit-nano/scikit-nano,scikit-nano/scikit-nano,androomerrill/scikit-nano