Nix files.

These new Nix files can be used as an alternative to the Stack-based
build.

Change-Id: I56ae4e27fa26541cd88583a7806f2834cb6a1735
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..520f11f
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,58 @@
+{
+  "nodes": {
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1627913399,
+        "narHash": "sha256-hY8g6H2KFL8ownSiFeMOjwPC8P0ueXpCVEbxgda3pko=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "12c64ca55c1014cdc1b16ed5a804aa8576601ff2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1629284811,
+        "narHash": "sha256-JHgasjPR0/J1J3DRm4KxM4zTyAj4IOJY8vIl75v/kPI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "c5d161cc0af116a2e17f54316f0bf43f0819785c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1629466665,
+        "narHash": "sha256-IZ726OdbYsdGxMa4Cae54jmfbTpgfFJRr5q7Fr7a4RM=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "63047a07e9c7f376803ff7f971fc951585f0bfae",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}