Nixcli

An advanced implementation of the CLI (command line interface) for nix. It supports the ```validate``` & ```dump``` commands. These commands are implemented as modules (= classes) ```Validate``` & ```Dump``` that both implement the interface (= virtual class) ```IModule```. Parsing of the cmd line is done with ```boost::program_options```.
The whole code is added as separate executable to ```CMakeLists.txt``` and resides in the ```Cli``` directory.
thanks good catch! That's an almost funny mistake, I shall call it the "random comma generator" :) But more seriously, I think this line should be removed as the modules should not output directly and it has no sense otherwise. If there are no objections Ill remove it.