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.wren

@@ -0,0 +1,18 @@
+// retoor <retoor@molodetz.nl>
+
+import "tempfile" for NamedTemporaryFile
+import "pathlib" for Path
+
+var tmp = NamedTemporaryFile.new()
+System.print(tmp.name is String) // expect: true
+System.print(Path.new(tmp.name).exists()) // expect: true
+System.print(tmp.closed) // expect: false
+System.print(tmp.delete) // expect: true
+
+tmp.write("hello tempfile")
+var content = tmp.read()
+System.print(content) // expect: hello tempfile
+
+tmp.close()
+System.print(tmp.closed) // expect: true
+System.print(Path.new(tmp.name).exists()) // expect: false