Propose additional units to the DDLm reference dictionary

[vaitkus]

The CIF_RAMAN dictionary version 0.3.3 uses several units of measurement that are not among the units allowed by the DDLm reference dictionary [1]. While currently there is no formal way of defining dictionary-specific units, the developers of DDLm are quite open to the idea of including the missing units in the reference dictionary (see discussion in issue [2]).

Additional units should be suggested in the form of a PR. Specifically, proper descriptions of the milliwatts, lines_per_millimetre and arbitrary_units units should be added to the templ_enum.cif file.

[1] https://github.com/COMCIFS/cif_core/blob/master/ddl.dic
[2] COMCIFS/cif_core#385