Add atom to the crystall.
If new_atom```s literal and index are the same as of some atom of the crystal,
then ``new_atom is not added.
If index of new_atom is not defined, it is set.
- Parameters:
- new_atoms
Atom New atom.
- relativebool, default False
Whether new_atom position is in relative coordinates.
- Raises:
- TypeError
If new_atom is not an Atom.
- ValueError
If the atom is already present in the crystal.