Separate yparser

This is one of the approaches we can take to fix the symbols loop between libknot and libknot-int.

This will work only in case that neither libknot nor libknot-int will use symbols from libknot-yparser.

Other options include depending on intended usage of yparser:

1. move yparser to libknot
2. merge libknot and libknot-int (but only expose libknot in default headers, e.g. #include <libknot.h> vs #include <libknot-int.h>). This will also need strict GCC Visibility definitions for symbols in libknot-int, so we don't have to bump SOVERSION often
3. move knot_dname as dname_* to libknot-int, but export them as knot_dname_* from libknot + use dname_* in yparser

O.