* Ported to Minecraft 1.13, with the power of Rift!

Additions:

* Scripting: The tag="<tag>" token, which matches tags.

Changes:

* StackUp scripts are now expected to be in data packs, "data/minecraft/scripts/<name>.stackup".
* The maximum stack size is now automatically decided upon by scanning all scripts.

Errata:

* No stack size rendering configuration! Rift doesn't yet have a configuration API, and I didn't feel like
  introducing a non-standard one myself.
