Use a more familiar builder API

[cyberdelia]

Use a more familiar builder API and Java methods name, essentially not exposing MacaroonsBuilder directly but via Macaroon.builder() methods, and changing the builders method to be more inline with Java naming conventions.

Macaroon macaroon = Macaroon.builder(location, secretKey, identifier)
    .addCaveat("time < 2042-01-01T00:00")
    .addCaveat("http://auth.mybank/", caveat_key, identifier)
    .build();

This also moves all static methods that returns a Macaroon directly has a static method of Macaroon itself:

Macaroon.create(location, secretKey, identifier);
Macaroon.deserialize(serialized);

This is entirely backward compatible for now, but all methods that would need to be changed or removed in the future have been marked as deprecated.