logilab-doctools #4448384 [rst2dbk] Add bibliographic field for document reference [in-progress]

When describing a document in ReST, we want to give the reference of the document (such reference is unique). No standard bibliographic field allows us to define this piece of information.

appeared in<not specified>
done in0.7.0
load left0.200
closed by<not specified>
patchAdding processing for additional bibliographic field containing the document reference [applied]