yin: Don't ignore attribute in hydrator if not present in the request

The Hydrator ignores attribute if they are not present in the request, the callable is never call.

This is annoying if an attribute is required for example. I think it should be great to execute all the callable and let the developer decide what it should do, ignore the attribute, set it to null, throw an exception, etc.

I made a commit on my repo https://github.com/lunika/yin/commit/d6955813bc7bc1839794ff445a75d222902e94d1

This is yet again a BC break. An example how ti use it :

    protected function getAttributeHydrator($user)
    {
        return [
            'firstname' => function ($user, $attributeValue, $data, $attribute, $isMissing) {
                if (true === $isMissing) {
                    throw new MissingMandatoryAttributeException($attribute);
                }

                $user['firstname'] = $attributeValue;

                return $user;
            },
            'lastname' => function ($user, $attributeValue, $data, $attribute, $isMissing) {
                if (false === $isMissing) {
                    $user['lastname'] = $attributeValue;
                }

                return $user;
            }
        ];
    }