Introduce Applicative Validation

[making]

This pr introduces an implementation similar to Vavr's Validation or Scalaz's Validation control class that is an applicative functor and facilitates accumulating errors.

ApplicativeValidator which can be obtained by Validator.applicative() has validate method and it returns Validation object as follows:

Validator<Email> emailValidator = ValidatorBuilder.of(Email.class)
                                                    .constraint(...)
                                                    .build()
                                                    .prefixed("email");
Validator<PhoneNumber> phoneNumberValidator = ValidatorBuilder.of(PhoneNumber.class)
                                                    .constraint(...)
                                                    .build()
                                                    .prefixed("phoneNumber");

Validation<ConstraintViolation, ContactInfo> validation = emailValidator.applicative().validate(email)
                                                                            .compose(phoneNumberValidator.applicative().validate(phoneNumber))
                                                                            .apply(ContactInfo:new);

// or

Validation<ConstraintViolation, ContactInfo> validation = Validations.compose(emailValidator.applicative().validate(email), phoneNumberValidator.applicative().validate(phoneNumber)))
                                                                            .apply(ContactInfo:new);


HttpStatus status = validation.fold(v -> HttpStatus.BAD_REQUEST, c -> HttpStatus.OK);

This API makes it possible to make different validation results composable.
It's more powerful than using ValidatorBuilder.nest() method for reusing a value object class.

closes gh-119

[making]

If it sounds natural, I'd like to change as follows:

• applicative() -> composable()
• ApplicativeValidator -> ComposableValidator

Validation<ConstraintViolation, ContactInfo> validation = Validations.compose(emailValidator.composable().validate(email), phoneNumberValidator.composable().validate(phoneNumber)))
                                                                            .apply(ContactInfo:new);

[making]

review comments in Japanese from @gakuzzzz
https://gist.github.com/gakuzzzz/6acd31a9c7d1756ae6c2745442720a79

[making]

If it sounds natural, I'd like to change as follows:

• applicative() -> composable()
• ApplicativeValidator -> ComposableValidator

Validation<ConstraintViolations, ContactInfo> validation = Validations.compose(emailValidator.composable().validate(email), phoneNumberValidator.composable().validate(phoneNumber)))
                                                                            .apply(ContactInfo:new)
                                                                            .mapError(ConstraintViolations::concat);;

From @gakuzzzz 's feed back in https://gist.github.com/gakuzzzz/6acd31a9c7d1756ae6c2745442720a79#gistcomment-3741084 , I'm going to go with applicative at this moment.