Add nix-shell for development

shell.nix

@@ -0,0 +1,12 @@
+{ pkgs ? import <nixpkgs> {} }:
+  pkgs.mkShell {
+    nativeBuildInputs = with pkgs.buildPackages; [
+      gnumake
+      libgcc
+      haskellPackages.SDL
+      haskellPackages.SDL-ttf
+      haskellPackages.SDL-gfx
+      haskellPackages.SDL-mixer
+      glew
+    ];
+}