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/tempfile/named_temporary_file_use.wren

@@ -0,0 +1,15 @@
+// retoor <retoor@molodetz.nl>
+
+import "tempfile" for NamedTemporaryFile
+import "pathlib" for Path
+
+var savedName = null
+
+NamedTemporaryFile.new().use {|tmp|
+    tmp.write("inside use block")
+    var content = tmp.read()
+    System.print(content) // expect: inside use block
+    savedName = tmp.name
+}
+
+System.print(Path.new(savedName).exists()) // expect: false