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_class_instance.wren

@@ -0,0 +1,50 @@
+// retoor <retoor@molodetz.nl>
+
+import "scheduler" for Scheduler, Future
+
+class Counter {
+    construct new(start) {
+        _value = start
+    }
+
+    value { _value }
+
+    add(n) {
+        var op = async { |x|
+            _value = _value + x
+            return _value
+        }
+        return await op(n)
+    }
+
+    subtract(n) {
+        var op = async { |x|
+            _value = _value - x
+            return _value
+        }
+        return await op(n)
+    }
+
+    reset() {
+        var op = async {
+            _value = 0
+            return _value
+        }
+        return await op()
+    }
+}
+
+var counter = Counter.new(10)
+System.print(counter.value) // expect: 10
+
+System.print(counter.add(5)) // expect: 15
+System.print(counter.value) // expect: 15
+
+System.print(counter.subtract(3)) // expect: 12
+System.print(counter.value) // expect: 12
+
+System.print(counter.reset()) // expect: 0
+System.print(counter.value) // expect: 0
+
+System.print(counter.add(10)) // expect: 10
+System.print(counter.subtract(3)) // expect: 7