feat: add await syntax for direct async function calls and new generator/phonebook apps

Add compiler support for calling async functions directly with `await fn(args)` syntax, automatically translating to `await fn.call(args)`. Introduce `create_merge` Makefile target for merging Wren source files. Include new `apps/generator.wren` source code generator using OpenRouter API, `apps/phonebook.wren` CLI phonebook with SQLite backend, and `apps/minitut.md` Wren tutorial reference. Update `example/await_demo.wren` with parameterized async functions, nested awaits, and expression usage. Fix JSON parsing in `example/openrouter_demo.wren` to strip markdown code fences. Document new await syntax in `manual/api/scheduler.html`.

test/await/await_fn_module_var.wren

@@ -0,0 +1,20 @@
+// retoor <retoor@molodetz.nl>
+
+import "scheduler" for Scheduler, Future
+
+var moduleDouble = async { |x| x * 2 }
+var moduleAdd = async { |a, b| a + b }
+
+class Helper {
+    static useModuleVar(x) {
+        return await moduleDouble(x)
+    }
+
+    static combineModuleVars(a, b) {
+        return await moduleAdd(await moduleDouble(a), await moduleDouble(b))
+    }
+}
+
+System.print(await moduleDouble(10)) // expect: 20
+System.print(Helper.useModuleVar(15)) // expect: 30
+System.print(Helper.combineModuleVars(5, 10)) // expect: 30