Handle CIF files from ICSD

[jonwright]

• strip charge states from atoms (Al0+ -> Al) and/or add the ionic form factors or investigate the _atom_type_symbol loop
• parse / check the symmetry, an example is below. The symmops listed should match the symmops from the internal tables in xfab.

_space_group_name_H-M_alt 'P -4 3 m'
_space_group_IT_number 215
loop_
_space_group_symop_id
_space_group_symop_operation_xyz
1 '-z, -y, x'
2 '-y, -x, z'
3 '-x, -z, y'
4 '-z, -x, y'
5 '-y, -z, x'
6 '-x, -y, z'
7 '-z, y, -x'
8 '-y, x, -z'
9 '-x, z, -y'
10 '-z, x, -y'
11 '-y, z, -x'
12 '-x, y, -z'
13 'z, -y, -x'
14 'y, -x, -z'
15 'x, -z, -y'
16 'z, -x, -y'
17 'y, -z, -x'
18 'x, -y, -z'
19 'z, y, x'
20 'y, x, z'
21 'x, z, y'
22 'z, x, y'
23 'y, z, x'
24 'x, y, z'
loop_
_atom_type_symbol
_atom_type_oxidation_number
Al0+ 0
Cu0+ 0