feat: add async/await keywords, Num/String extensions, and Jinja markdown example

Add `async` and `await` token support to the Wren compiler with scheduler resolution logic, extend `Num` with `e` constant, hyperbolic trig, base conversion, and new methods (`isZero`, `gcd`, `lcm`, `digits`, etc.), extend `String` with `lower`, `upper`, `capitalize`, `title`, and regenerate `wren_core.wren.inc`. Include `Makefile` for multi-platform builds, rewrite `README.md` with updated build instructions, and add `example/await_demo.wren` and `example/jinja_markdown.wren` demonstrating new features.

test/await/in_method.wren

@@ -0,0 +1,11 @@
+import "scheduler" for Scheduler
+import "timer" for Timer
+
+class Helper {
+  static run() {
+    await Timer.sleep(1)
+    return "completed"
+  }
+}
+
+System.print(Helper.run()) // expect: completed