Irccd: finish custom IRC library, closes #581 Finally remove the lovely libircclient that has been used since the beginning of irccd back in 2013. Several issues made the choice of developing a custom IRC library: - libircclient requires select(2) system call and works in procedural paradigm which is incompatible with our Boost.Asio main loop, - there was no way in the libircclient to detect custom message like PING to handle dead servers, this required to bundle the library within the application, - the library use static output buffer which requires to keep an internal queue of commands that we flush at each iteration.