Rename `Nbt` to `BinaryNbt`, and `NbtFormat` to `Nbt`, and add `Nbt` companion object for `NbtTag` serialization

[BenWoodworth]

It would be nice to have default functionality common to binary/stringified NBT accessible with Nbt.[...], but the current NbtFormat/Nbt/StringifiedNbt naming doesn't work nicely with that.

Brief rationale:

• Having Nbt.[...] for the API feels nicer from a naming perspective for basic un-configured serialization
• This API could be added under the current (binary) Nbt class
  • but the companion object would implement NbtFormat, and it feels awkward/unexpected to be a different configuration type
• This API could be added to the NbtFormat interface as a companion object
  • but it feels awkward/unexpected to have to write NbtFormat.encodeToNbtTag(serializer, value)
• It feels better to me to have the Nbt class represent the general structure for the format, dealing with the in-memory representation and the NbtTag classes.
  • It would be an actual concrete & usable API, instead of just a parent interface for shared functionality.
  • Then, have more types of Nbt named according to what functionality they bring (BinaryNbt and StringifiedNbt).
• This new naming means all general NBT API is named Nbt-, while binary/stringified API are BinaryNbt- and StringifiedNbt-, making the API easier to find through intellisense, and grouping code files more nicely when alphatized.