Java Edition 1.12-pre1

1.12-pre1 is the first pre-release released for 1.12.

Additions

 * Advancements
 * Added new advancements:
 * "A Furious Cocktail"
 * "Postmortal"
 * "Subspace Bubble"
 * "Uneasy Alliance"

Changes

 * Advancement trees are now centered in the UI
 * Optimized the recipe book
 * Items & entities in advancements have an extra "nbt" field (string nbt, like in commands)
 * Entities in advancements have an extra "effects" and "location" field
 * Added new "effects_changed", "used_totem", "nether_travel" advancements triggers
 * Removed "commands" from advancement rewards
 * Removed "arbitrary_player_tick" advancement trigger
 * Added "function" to advancement rewards
 * Added new "function" system, plaintext files in world/data/namespace/file.txt
 * Functions are a list of commands, one line per command, with //comment (or #comment) support
 * Added new "/function namespace:file" command
 * Added new gamerule "gameLoopFunction", a function to be executed once per tick
 * Added "hidden" field to advancement display info, defaults to false