Implement simple api example

[Daniel-Boll]

closes #1

[Daniel-Boll]

For the sake of simplicity of the Proof of Concept I manage only to make a simple app, by now with the design decision of using a class to instantiate the app and that don't expect any callbacks.

import { AxumApp } from "./index";

const app = new AxumApp();

app.get("/");

app.listen(3000);

❯ http :3000
HTTP/1.1 200 OK
...
Hello World!