produce grammars from bison files

This ticket is about the old idea to produce ABNF grammars from the bison files, so for client class expressions, and DHCPv4 / DHCPv6 / D2 / CA / Netconf server/agent configuration files.

Should be based on https://stackoverflow.com/questions/19477103/extract-bnf-grammar-rules-from-yacc-file