Replace konstraint extensions by a validator Kotlin DSL

In order to provide a more idiomatic Kotlin experience, I am wondering if we could replace konstraint extensions introduced by #16 (I don’t really like this kind of k prefixed to be honest) by a Kotlin DSL that would isolate more the Kotlin API from the Java one. I need to give it more thoughts but my initial proposal is the following:

val validator = validator<User> {
     constraint(User::name) {
          notNull()
          lessThanOrEqual(20)
     }
     constraint(User::email) {
          notNull()
          greaterThanOrEqual(5)
          lessThanOrEqual(50) //
          email()
     }
     constraint(User::age) {
          notNull()
          greaterThanOrEqual(0)
          lessThanOrEqual(200)
     }
}

Any thoughts? If you like it I can probably try to craft a PR.

[hartmut-co-uk]

let me try to make time! (might not be within the next 2 weeks)

[making]

Supported by 0329aa47f67c4071adc3cc576f9287faaddbdde7 🎉