extend the Freedict schema to handle new demands

[bansp]

This issue rides on the back of #62 (update of the ODD).

One issue is to introduce a fixed list of types for <pron>, with @type="broad" set as the default (see this message for some background and links; the follow-ups provide some further explanation).

Yet another, that came to my mind at some point, is to import some lists of values of the @type attribute from the TEI Lex0, for "usg", for example. That may involve the modification of the existing databases, or the Freedict-local type values can simply get added to that fixed list.

I'm guessing that this is all up to the demands of the current databases and to the general standardization practice. So perhaps this ticket can serve to gather a list of demands, or at least a list of references to other issues.