Ability to clone NBT tags, as well as new 1.13.x classes
Support for Java optionals and 1.13.x particles
Bug Fixes
Fixed an issue with the component array converter
Fixed an issue reloading (still not recommended)
Fixed an issue with 1.8.0 support
Fixed an issue with the Bukkit updater, treat Paper as "Spigot"
Fixed an issue where the byte buffer in a WirePacket was not released
Improvements
Java 9/10 support (still not recommended due to reflection performance)
Reworked internal conversion and cloning logic to be cleaner and more efficient
Replaced MCstats (RIP) with bStats
More consistent packet metadata API
Handle AIR item stacks properly
Use real players wherever possible instead of temporary players
Note to developers: This will be the last release of the ProtocolLib-API module. Lots of people have been having issues with the plugin failing to load, and the best solution I see is to recombine the modules. Resuming with 4.5.0, use ProtocolLib as a whole as your dependency.