World folder is the source of truth

- actor/<id>/ holds actor.wasm, actor.json, source/, public/, data/, versions/
- the broker boots by scanning actor/; a changed actor.wasm is an upgrade,
  a rejected one stays in versions/ with a reason and the files come back
- /actor hides every data/ folder
- subscriptions live in the subscriber's actor.json
- cargo installs the SDK and points sausage-actor at it; no build limits
- PROTOCOL.md

examples/crasher/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "crasher"
+version = "0.1.0"