Nix support & automated update (#130)

* Add a nix flake

* Update flake deps and nix package's version nightly

* nix-flake: Update vendorSha256 on each push

An extra commit will be pushed only if needed

* Move flake.* into root directory

Update flake.lock

* nix-flake: Support more systems, commit hash as version

* Don't automatically update flake.lock

flake.lock

@@ -0,0 +1,26 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1655221618,
+        "narHash": "sha256-ht8HRFthDKzYt+il+sGgkBwrv+Ex2l8jdGVpsrPfFME=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "6616de389ed55fba6eeba60377fc04732d5a207c",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "ref": "nixos-unstable",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}