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.

Makefile

@@ -0,0 +1,15 @@
+# retoor <retoor@molodetz.nl>
+
+.PHONY: build tests clean debug
+
+build:
+	cd projects/make && $(MAKE) -f wren_cli.make -j $$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)
+
+debug:
+	cd projects/make && $(MAKE) -f wren_cli.make config=debug_64bit -j $$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)
+
+tests: build
+	python3 util/test.py
+
+clean:
+	cd projects/make && $(MAKE) -f wren_cli.make clean