Initial implementation of RR type descriptors. It's more or less a simplified copy from NSD, will need changes and maybe more API functions.

Only test for creating RRSet is implemented. Did not try to run it
  nor to compile it. Just an outline yet.

refs #109

Were not checking for NULL pointers.

refs #88

Just basic functions declared:
- creating node
- destroying node
- adding RRSet
- getting RRSet
- getting parent of a node

refs #88

API completed, compilable. Will have to change manipulation with rdata as does not use its API as it should.

RDATAs will be stored in a ordered cyclic list.
Information about RRSet's signatures reflects this.

Added some basic API functions for manipulating the structure and
  comments to describe their intended behaviour.

TODO: Need to define some function for comparing RDATAs.

refs #88

Destructor functions now take ** to set the given pointer to NULL.
RDATA structure now contains pointer to next RDATA, so they may
  create a linked list. (Will be used in RRSet).

Added file comments and \addtogroup statements.

Modified tests accordingly.

refs #88

refs #88, #31

A lot of syntax fixes (sorry, was not compileable before).

refs #88

Tests implemented so far:
- create empty
- create non-empty
- set_item() for setting RDATA items one-by-one

TODO:
= set_items()

refs #88, #31

Tests were not freeing memory.
Replaced forgotten printf by debug routine in dname.c.

refs #88, #31

- creating RDATA structure (empty, possibly with reserving space)
- setting and getting particular items
- setting all items (only if empty)
- deallocating

refs #5, #88

Tests of all API functions implemented, except for
  dnslib_dname_free() - no way to test that yet (consider using
  storage allocation hooks:
  http://www.cs.utah.edu/dept/old/texinfo/glibc-manual-0.02/library_3.html#SEC30
  )

refs #5, #31

dname and node were referencing each other. Used
  forward-declaration of node in dname.
Added API getter functions (with implementation):
  - dnslib_dname_name()
  - dnslib_dname_size()
  - dnslib_dname_node()
Fixed dname implementation:
  - str_to_wire() was replacing chars by label lengths
  - new_from_str() bad assert
  - new_from_wire() was not allocating space for the name
  - to_str() was de facto copying the wire format

Added some debug output to dname

refs #5, #88

refs #5, #88

Fixed creating dname struct from wire format (was not copying).
refs #5, #88

- creating dname (empty, from string, from wire format)
- deleting dname
- converting dname to string

Minor change in node - added linked list pointer to next node.

refs #5, #88

refs #5, #88

refs #5

* Test now detects invalid number of parameters.