added zmcat

pkgs/default.nix

 {
   hostPkgs        ? import <nixpkgs> {},
   system          ? builtins.currentSystem,
+  pkgs-stable     ? import ../pin.nix { inherit hostPkgs; jsonpath=../nixpkgs-18.03.json; depset = {inherit system;}; },
   pkgs            ? import ../pin.nix { inherit hostPkgs; jsonpath=../nixpkgs-unstable.json; depset = {inherit system;}; },
   kapack          ? import ../pin.nix { hostPkgs = pkgs ; jsonpath=../kapack.json; depset = {hostPkgs=pkgs;};},
  supportedSystems ? [ "x86_64-linux" "i686-linux" ]
@@ -92,6 +93,8 @@ let
           cc = icc;
       });
     };
+
+    zmcat = pkgs-stable.haskellPackages.callPackage ./tools/zmcat {};
   };
 
 in argopkgs // pkgs

pkgs/tools/zmcat/default.nix

+{ fetchFromGitHub, mkDerivation, base, bytestring, stdenv, zeromq4-haskell }:
+   mkDerivation {
+     pname = "zmcat";
+     version = "0.2";
+
+     src = fetchFromGitHub {
+       owner = "freuk";
+       repo = "zmcat";
+       rev = "master";
+       sha256 = "1lvzb989gzj95mycnx8j1dck8asa85brspq8z492jm1rzgkc1qn7";
+     };
+
+     isLibrary = true;
+     isExecutable = true;
+     libraryHaskellDepends = [ base bytestring zeromq4-haskell ];
+     executableHaskellDepends = [ base bytestring ];
+     homepage = "https://github.com/lucasdicioccio/zmcat";
+     description = "Command-line tool for ZeroMQ";
+     license = stdenv.lib.licenses.bsd3;
+   }