Add independent Rust engine, deterministic mod API and asset pipeline

examples/mods/aurora/scripts/cell.rhai

@@ -0,0 +1,11 @@
+fn on_pickup(event, state, random) {
+    let recovered = if state.contains("recovered") { state.recovered + 1 } else { 1 };
+    #{ commands: [#{ op: "credits", amount: 25 }], state: #{ recovered: recovered } }
+}
+
+// A selected repair cell can also be consumed with the special-action button.
+fn on_use(event, state, random) {
+    let used = if state.contains("used") { state.used + 1 } else { 1 };
+    state.used = used;
+    #{ commands: [#{ op: "objective", key: "aurora:repairs_used", value: used }], state: state }
+}

examples/mods/aurora/scripts/drone.rhai

@@ -0,0 +1,16 @@
+fn on_spawn(event, state, random) {
+    #{ commands: [], state: state }
+}
+
+fn on_tick(event, state, random) {
+    // on_tick may be queued on the same step as on_death; do not command a retired entity.
+    if event.health <= 0 { return #{ commands: [], state: state }; }
+    let sideways = if (event.tick / 24) % 2 == 0 { 1 } else { -1 };
+    #{ commands: [#{ op: "velocity", entity: event.entity, vx: sideways, vy: 1 }], state: state }
+}
+
+fn on_death(event, state, random) {
+    let destroyed = if state.contains("destroyed") { state.destroyed + 1 } else { 1 };
+    #{ commands: [#{ op: "objective", key: "aurora:destroyed", value: destroyed }],
+       state: #{ destroyed: destroyed } }
+}

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 }
+}

examples/mods/aurora/scripts/weapon.rhai

@@ -0,0 +1,13 @@
+// The normal centre projectile is emitted by the engine. Add two angled pulses.
+fn on_fire(event, state, random) {
+    let shots = if state.contains("shots") { state.shots + 1 } else { 1 };
+    let spread = 1 + random[0] % 2;
+    #{ commands: [
+        #{ op: "projectile", weapon: "aurora:pulse_projectile", x: event.x - 6, y: event.y, vx: -spread, vy: -8 },
+        #{ op: "projectile", weapon: "aurora:pulse_projectile", x: event.x + 6, y: event.y, vx: spread, vy: -8 }
+    ], state: #{ shots: shots } }
+}
+
+fn on_hit(event, state, random) {
+    #{ commands: [#{ op: "effect", x: event.x, y: event.y }], state: state }
+}