- Removed dependency on stuff from common.h (some macros moved to
  dnslib/dnslib-common.h, debug macros moved to dnslib/debug.h).
- Moved required modules from lib/ to dnslib/ext/ (dynamic array,
  skip list, base32hex encoding).
- Moved whole cuckoo hashing to dnslib (dnslib/hash/)

Currently, dnslib is only dependent on stuff from alloc/, which
should be separated as a standalone library.

refs #400