config.hh: Add documentation
config.hh: Add documentation

Provides some general overview on the mechanics of Config/Setting and
comments for the public methods of Config.

NixOS/nix,NixOS/nix,rycee/nix,NixOS/nix,rycee/nix,rycee/nix,NixOS/nix,rycee/nix,rycee/nix,NixOS/nix