• Remame am.ik.yavi.builder.Yavi => am.ik.yavi.builder.ValidatorBuilderExtensions
• Add constraintOnGroup in ValidatorBuilderExtensions
• Add followings coroutines variants of Either methods (#14)
  • EitherExtensions.awaitFold
  • EitherExtensions.awaitBimap
  • EitherExtensions.awaitLeftMap
  • EitherExtensions.awaitRightMap
• Add EitherExtensions.leftOrNull() and EitherExtensions.rightOrNull (#15)
• Make doOnLeft and doOnRight return itself