Provide defaults to unimplemented methods in endpoints for App style api.

[Tesseract22]

Make get, post, ... methods optional in endpoint. Check whether these method exist at comptime. When no corresponding method is provided, the handler simply return immediately.

Since it uses comptime, hopefully it should not add any checks at runtime.

Also since App shares a global state (_static), I think it makes more sense NOT accept an app instance in the apis. So:

old:

var app = App.init(...);
try app.register(...);

proposal:

App.init(...);
App.register(...);

See examples/app/.

[renerocksai]

Awesome! And sorry for the delay. The App stuff is a bit confusing wrt the Zig convention TypeName, instance_name, but I think I can live with that 😄.