Add Nix shell configuration for compiling using Nix (#760)

* Add Nix shell configuration for compiling using Nix

This adds a Nix development shell configuration for using the Nix
package manager. Please see the pull request with this commit attached
for more information on how exactly it works.

* Add name attribute to shell

shell.nix

@@ -0,0 +1,42 @@
+{ }:
+let
+  pkgs = import (builtins.fetchTarball {
+    url = "https://github.com/NixOS/nixpkgs/archive/c407032be28ca2236f45c49cfb2b8b3885294f7f.tar.gz";
+  }) { };
+
+  libs =
+    with pkgs;
+    [
+      SDL2
+      pkg-config
+      openal
+      alsa-lib
+      libvlc
+      libpulseaudio
+      libGL
+    ]
+    ++ (with xorg; [
+      libX11
+      libXext
+      libXinerama
+      libXi
+      libXrandr
+    ]);
+in
+pkgs.mkShell {
+  name = "CodenameEngine";
+
+  packages = with pkgs; [
+    haxe
+    neko
+    libsForQt5.qttools
+  ];
+
+  buildInputs = libs;
+
+  LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath libs;
+
+  shellHook = ''
+    source update.sh
+  '';
+}