Add @Nullable to NbtValued methods.
Remove DataException from NbtValued's setNbtData().
Use Location.getYaw() and getPitch() for converting to Bukkit Locations.
Have BukkitEntity.getState() return null for now.
Add new Bukkit implementation adapter system to access MC internals.

Replaces the old NMSBlocks.
Fix blocks.json not being placed in the distribution.