fixes #331

Separate yparser

This is an attempt to unloop the library dependency loop.

1. libknot-int is now standalone library and no symbols from libknot are used.
2. libknot depends on libknot-int
3. libknot-yparser depends on libknot and libknot-int

@dsalzman and @jvcelak please review.

As a side note - I think there should be a libknot/libknot.h that would be enough to include in any project using libknot, dtto for libdnssec...

Edit: there is libknot/libknot.h, it's just not used that much...

See merge request !350