RockPaperScissors: Server and Client mode

It's sad to say that I break all the written and unwritten rules of using git.
This commit contains a bunch of changes, including almost full rewrite of the
actual source code. Begging for pardon, I thoroughly list the changes below:
* Added -g option to CMakeLists.txt to build debug binaries
** Should be optional.
* Added boost::program_options to CMakeLists.txt to use as a command line argument parser.
* Added pthread link target to CMakeLists.txt because boost::asio needs it (on Unix).
** Should be branched to support both Windows and Linux.

* The program introduces fancy command line options (see --help for details).
* The program introduces so-called "server" and "client" modes.
* The program in server mode listens to any address for incoming connection (ignores specified address).
* The program features better error checking.