Code cleanup (octet strings)

[sdecugis]

Some cleanup is needed in the code:

• for all data coming from the network (Diameter Id, Session Id, ...) use octet string types everywhere (uint8 * + size_t).
• Create a quick function to compare octet strings based on the length first, then on the contents. This will speed many operations. The only limitation is that it is difficult to find if a string is the prefix of another (but we do not use this).

This will impact a large part of the code, and will be performed only after the first release.

[sdecugis]

Another major cleanup to perform (names are temporary):

• rename libfreediameter to libfdprotocol
• create a new libfdnetwork and move the network functions and peers functions from daemon to there
• create a new libfd and move all other daemon's functions except command-line parsing there
• the daemon becomes a very light file that only calls the libfd functions. This way, other projects can re-use the freediameter code more easily.

[sdecugis]

Restructured since 658

New ctetstring handling introduced in 706