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.

manual/api/io.html

@@ -40,6 +40,8 @@
                     <span class="section-title">API Reference</span>
                     <ul>
                         <li><a href="index.html">Overview</a></li>
+                        <li><a href="string.html">String</a></li>
+                        <li><a href="number.html">Num</a></li>
                         <li><a href="http.html">http</a></li>
                         <li><a href="websocket.html">websocket</a></li>
                         <li><a href="tls.html">tls</a></li>
@@ -58,6 +60,7 @@
                         <li><a href="datetime.html">datetime</a></li>
                         <li><a href="timer.html">timer</a></li>
                         <li><a href="io.html" class="active">io</a></li>
+                        <li><a href="pathlib.html">pathlib</a></li>
                         <li><a href="scheduler.html">scheduler</a></li>
                         <li><a href="math.html">math</a></li>
                     </ul>
@@ -274,7 +277,7 @@ backup.call("important.txt")</code></pre>
 
             <footer class="page-footer">
                 <a href="timer.html" class="prev">timer</a>
-                <a href="scheduler.html" class="next">scheduler</a>
+                <a href="pathlib.html" class="next">pathlib</a>
             </footer>
         </main>
     </div>