…FS#67.

Specifically, examples were added for the
`_atom_site_moment_Fourier_param.modulus_symmform`,
`_atom_site_moment_Fourier_param.phase_symmform` and
`_atom_site_moment_Fourier_param_sin_symmform` data items.

The previous example was replaced by examples provided in issue COMCIFS#67.
The previous value was merge with the example of the
ATOM_SITE_MOMENT_FOURIER_PARAM category. The category example was only slightly
modified by replacing the dotless data names with their dotted counterparts
and correcting several symmform values that lacked a trailing modulation
number.

…nitions.

…OMCIFS#67.

The symmform symbolic expression description part was copied from the
definition of `_atom_site_moment_Fourier_param.cos_symmform` and adapted to
better reflect the syntax of each individual item.

As specified in
COMCIFS#67 (comment),
the 4th character is a numeric code as specified in the
_atom_site_moment_Fourier.wave_vector_seq_id data item.