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.

example/jinja_markdown.wren

@@ -0,0 +1,67 @@
+// retoor <retoor@molodetz.nl>
+
+import "jinja" for Environment, DictLoader
+
+System.print("=" * 60)
+System.print("JINJA MARKDOWN - Markdown/HTML Conversion in Templates")
+System.print("=" * 60)
+
+var templates = {
+  "md_to_html": "{\% markdowntohtml \%}# {{ title }}
+
+{{ description }}
+
+- Item **one**
+- Item **two**
+- Item **three**
+{\% endmarkdowntohtml \%}",
+
+  "html_to_md": "{\% markdownfromhtml \%}<h1>{{ title }}</h1>
+<p>This is a <strong>paragraph</strong> with <em>formatting</em>.</p>
+<ul>
+<li>First</li>
+<li>Second</li>
+</ul>{\% endmarkdownfromhtml \%}",
+
+  "filter_md": "{{ content|markdown }}",
+
+  "filter_fromhtml": "{{ content|markdownfromhtml }}",
+
+  "mixed": "<div class=\"article\">
+{\% markdowntohtml \%}## {{ article.title }}
+
+{{ article.body }}
+{\% endmarkdowntohtml \%}
+</div>"
+}
+
+var env = Environment.new(DictLoader.new(templates))
+
+System.print("\n--- Markdown to HTML (block tag) ---")
+System.print(env.getTemplate("md_to_html").render({
+  "title": "Welcome",
+  "description": "This is a *template* with markdown support."
+}))
+
+System.print("\n--- HTML to Markdown (block tag) ---")
+System.print(env.getTemplate("html_to_md").render({
+  "title": "Documentation"
+}))
+
+System.print("\n--- Markdown filter ---")
+System.print(env.getTemplate("filter_md").render({
+  "content": "**Bold** and *italic* text."
+}))
+
+System.print("\n--- Markdown from HTML filter ---")
+System.print(env.getTemplate("filter_fromhtml").render({
+  "content": "<h2>Section</h2><p>A paragraph.</p>"
+}))
+
+System.print("\n--- Mixed HTML and Markdown ---")
+System.print(env.getTemplate("mixed").render({
+  "article": {
+    "title": "Getting Started",
+    "body": "Read the **documentation** for details."
+  }
+}))