Implement a higher level API

[alranel]

This package should also expose a higher level API that would do most of the stuff implemented in example/service.go.

A good example for that is https://github.com/italia/spid-perl-dancer2 (see its example app).

[alranel]

But what web framework would we use? net/http? goji? Maybe we should try to be compatible with any web framework that supports http.Handler, thus creating a bit less high level API but not creating strong lock-ins with any particular web framework.