Create validation rule for Hash Id

[EriBloo]

Hi. I created this validation rule for my own purpose and I would like to contribute it to your package if it complies with your standards. I guess it's not the cleanest way to validate, but it works properly.

There is another commit I would like you to include (I guess even if you don't want this validation rule) that fixes an exception if you try to decode improper HashId. This is a valid hash for my salt: XvKGYlLgyARBM. If I change any character (eg. XaKGYlLgyARBM) keyFromHashId would thrown an Undefined array key exception.