examples: add initial ecs-app

This is a temporary application to begin iterating on high-level ECS applications.

Eventually, this will be removed - for now it's just here so we can see how this API
looks today and improve it.

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

examples/ecs-app/renderer.zig

@@ -0,0 +1,13 @@
+const mach = @import("mach");
+const ecs = mach.ecs;
+
+pub const module = ecs.Module(.{
+    .components = .{
+        .location = Vec3,
+        .rotation = Vec3,
+    },
+    // TODO: there would be systems that we register here. Functions that iterate over entities
+    // with renderer components like `.geometry` and render them for example!
+});
+
+pub const Vec3 = struct { x: f32, y: f32, z: f32 };