starter: Add new bison/flex based parser for ipsec.conf

starter: Add new bison/flex based parser for ipsec.conf

The parser simply returns key/value pairs of all sections, it already
resolves also= and allows overriding options in all included sections
(not only %default), options set in included section can also be cleared
again (key=).
It provides other improvements too, like quoted strings (with escape
sequences), unlimited includes and better whitespace/comment handling.