Support simple key-value store

In order to persist my access and refresh tokens, I needed a store. I think
using a database like SQLite may have been fine for this but was heavier weight
than what I wanted.

I decided to write a simple key-value store when the state is encoded and JSON
in a file called kv.json.

TODO:
- Support field nesting
- Support better error handling
- Support parameterizing the store path (i.e. ./kv.json)

gopkgs/kv/default.nix

@@ -0,0 +1,11 @@
+{
+  depot ? import <depot> {},
+  ...
+}:
+
+depot.buildGo.package {
+  name = "kv";
+  srcs = [
+    ./kv.go
+  ];
+}