Add extra dispersion coeffs

[rowlesmr]

Probably a stretch too far, but I wrote some code to automate the formatting of the coefficients.

Now matches values given in Table 4.2.6.8 in ITC 2004

[vaitkus]

It is always nice to have parameters in a more machine readable form, however, I don't think that the template dictionary is the place for them unless they these values are actually imported by other dictionaries. It would probably be best to first decide if it would make sense to expand the coreCIF dictionary with new data items like _atom_type_scat.dispersion_real_Ti, etc.

In any way, having the ENUMERATION_SOURCE loop for these save frames would be useful.

[vaitkus]

Do we now need the _atom_type_scat.dispersion_real_Ti, _atom_type_scat.dispersion_real_Au, etc. data items in coreCIF that import these save frames?

[jamesrhester]

It looks like it would be more economical to create a data name _atom_type_scat.dispersion_real_by_target that does an indexed lookup on the target atom name e.g. [Pt Ag] would hold the dispersion for Pt at the wavelength of an Ag source. We'd fiddle with the dREL in atom_type_scat.dispersion_real to figure out whether or not we can do a lookup.