Rename UlidBasedGuidCreator to UlidSpecCreator
Add method UlidCreator.fromString()
Add RandomStrategy for UlidSpecCreator
Add DefaultRandomStrategy using thread local SecureRandom
Add OtherRandomStrategy for any instance of Random
Add tests cases
Optimize UlidConverter.fromString()
Optimize UlidConverter.toString()
Optimize UlidValidator.isValid()
Optimize UlidSpecCreator
Update README.md
Update tests cases