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/pathlib/rename.wren

@@ -0,0 +1,19 @@
+// retoor <retoor@molodetz.nl>
+
+import "pathlib" for Path
+
+var dir = Path.new("/tmp/wren_pathlib_test_rename")
+if (dir.exists()) dir.rmtree()
+dir.mkdir()
+
+var src = dir / "source.txt"
+src.writeText("content")
+System.print(src.exists()) // expect: true
+
+var dst = dir / "dest.txt"
+src.rename(dst)
+System.print(src.exists()) // expect: false
+System.print(dst.exists()) // expect: true
+System.print(dst.readText()) // expect: content
+
+dir.rmtree()