Include generated examples

[bvanelli]

It it's extremely nice to load examples when building an API, since the OpenAPI specification is going to contain an example value from the actual response. If you are building a validator for an actual object, you know more or less how the data should look like. Here are the relevant docs for this feature: https://fastapi.tiangolo.com/tutorial/schema-extra-example/

This MR adds another customizer to include the examples when generating the model. Here is a preview:

Of course, when presented with multiple options, it will pick the first:

Closes #14

Suggested and implemented during a Hackergarten: https://www.meetup.com/pt-BR/hackergarten-stuttgart/, thanks everyone who participated 😃