3.0.0-beta01

• Enum-like classes are generated by a source generator instead of using reflection. The source gen is generates the constructor and "CreateInvalidItem" as well.
• The name of the key property can be changed, i.e. be something different than "Key"
• There are 2 types of enum: IEnum and IValidatableEnum
• IValidatableEnum can be a struct as well, i.e. not just a class
• Added source generator for immutable value types
• Added partial method ValidateConstructorArguments to validate the ctor arguments
• Added roslyn analyzer and code fixes for better experience