mpg123: add conplay script

Available in the 'conplay' output.
'conplay' can seamlessly play audio books using mpg123.

pkgs/applications/audio/mpg123/default.nix

@@ -1,5 +1,9 @@
 { stdenv
-, fetchurl, alsaLib
+, fetchurl
+, makeWrapper
+
+, alsaLib
+, perl
 }:
 
 stdenv.mkDerivation rec {
@@ -10,12 +14,30 @@ stdenv.mkDerivation rec {
     sha256 = "02l915jq0ymndb082g6w89bpf66z04ifa1lr7ga3yycw6m46hc4h";
   };
 
-  buildInputs = stdenv.lib.optional (!stdenv.isDarwin) alsaLib;
+  outputs = [ "out" "conplay" ];
+
+  nativeBuildInputs = [ makeWrapper ];
+
+  buildInputs = [ perl ] ++ stdenv.lib.optional (!stdenv.isDarwin) alsaLib;
 
   configureFlags = stdenv.lib.optional
     (stdenv.hostPlatform ? mpg123)
     "--with-cpu=${stdenv.hostPlatform.mpg123.cpu}";
 
+  postInstall = ''
+    mkdir -p $conplay/bin
+    mv scripts/conplay $conplay/bin/
+  '';
+
+  preFixup = ''
+    patchShebangs $conplay/bin/conplay
+  '';
+
+  postFixup = ''
+    wrapProgram $conplay/bin/conplay \
+      --prefix PATH : $out/bin
+  '';
+
   meta = {
     description = "Fast console MPEG Audio Player and decoder library";
     homepage = http://mpg123.org;