Support exporting Hibernate Validators info

Most Java POJOs these days use Hibernate Validators to annotate fields: NotNull, NotEmpty, Size, Min, Max, regex pattern, etc.

That is badly missing information in the exported JSON schema, which makes contract definition via JSON incomplete.

Since Validators are pretty much a part of the standard Java stack by now, would be great if this module could read all the validators and export info about them for every field.