Implement hashCode/equals/toString methods in type classes

[don-vip]

Classes in co.elastic.clients.elasticsearch._types do not implement the hashCode/equals/toString methods

This would be particularly useful for debugging or in unit tests, could the generator be improved to generate these methods?

[swallez]

Thanks for the suggestions @don-vip!

toString has already been mentioned in #97 and indeed is a useful addition. We'll add it in a future version by serializing the type to JSON rendered in a string.

hashCode and equals are different beasts though, as they require additional code in every class. They may come in a later release.