Add independent Rust engine, deterministic mod API and asset pipeline

examples/mods/aurora/scripts/mission.rhai

@@ -0,0 +1,10 @@
+fn on_mission_start(event, state, random) {
+    #{ commands: [
+        #{ op: "give_item", item: "aurora:pulse_cannon", count: 1 },
+        #{ op: "objective", key: "aurora:destroyed", value: 0 }
+    ], state: state }
+}
+
+fn on_mission_end(event, state, random) {
+    #{ commands: [#{ op: "objective", key: "aurora:trial_finished", value: 1 }], state: state }
+}