Support Enum serialization

[BenWoodworth]

Minecraft appears to encode all enum-like values as an ordinal, so consider doing the same with enum values instead of throwing an "unsupported" error.

[BenWoodworth]

Minecraft seems to use TAG_Byte and TAG_Int for enums, so there doesn't seem to be an obvious default. It might be better to leave it up to the serializer to decide. Or perhaps some kind of @NbtEnum annotation to make it easy.

[Ayfri]

I like the idea of @NbtEnum, it should have a parameter to decide which type to use !