Fixed confusion between real esd values and s.u.s

[nautolycus]

This is designed to fix BUG #2

File now passes the dictionary syntax and semantics checks.

[vaitkus]

@nautolycus Also, maybe the name and description of _restr_plane_class.displacement_avsu should also be reverted? It seems to differ from the DDL1 version (https://github.com/COMCIFS/DDL1-legacy-dictionaries/blob/main/dictionaries/cif_core_restraints.dic) where it is defined as esd:

    _name                      '_restr_plane_class_displacement_esd'
   # ...
    _definition
;              The observed estimated standard deviation of the
               atoms from this plane.
;

[nautolycus]

@nautolycus Also, maybe the name and description of _restr_plane_class.displacement_avsu should also be reverted?

Certainly - thanks for spotting this.

[vaitkus]

Looks good, thanks!