Make RR TTL field 4 bytes

See merge request !31

By default pip doesn't allow system wide package installation anymore.
We need to create a virtual environment now to download and use apkg in
OBS publishing scripts.

CLI tools for C-DNS file inspection

See merge request !30

cdns-items command line tool prints full contents of individual
Query/Response, Address Event Count and Malformed Message items in
a C-DNS file.

cdns-blocks command line tool prints summary information about
individual Blocks in C-DNS file.

cdns-preamble command line tool prints human readable contents of
C-DNS file preamble.

cdns-itemcount command line tool prints the counts of Query/Response,
Address Event Count and Malformed Message items in a C-DNS file.

cdns-merge command line tool merges multiple C-DNS files into one.
It can only merge files with compatible 'major.minor.private' version.

Add string() method to all structures and classes representing C-DNS file
components to get human readable string representation of their
contents.

Add Python bindings generated by pybind11

See merge request !29

With this change installation path for Python bindings will take
DESTDIR into consideration when running 'make install'.

Initial implementation of Python bindings for library's whole API
generated by pybind11.

Apkg compat level 3

See merge request !28