Allow super simple keymap keycode definitions (very QMK-ish)

kmk/common/util.py

@@ -0,0 +1,10 @@
+def flatten_dict(d):
+    items = {}
+
+    for k, v in d.items():
+        if isinstance(v, dict):
+            items.update(flatten_dict(v))
+        else:
+            items[k] = v
+
+    return items