feat: Support kotlin's value classes

[Chuckame]

New features:

• Handle any primitive value and @Contextual as map keys #114

Breaking changes:

• @AvroInline removed as it is replaced by kotlin's value classes
• Stop supporting @AvroFixed on classes, works only on properties
• Stop supporting @ScalePrecision on classes, works only on properties
• Stop supporting @AvroDefault on classes, works only on properties