Reduce number of LivingEntity collision checks.
Better + more flexible itemstack merging
Only count entities in chunks being processed for the spawn wave. Fixes mob spawn issues.

Conflicts:
	src/main/java/net/minecraft/server/SpawnerCreature.java
Send maps a lot less often to combat the lag they cause. TODO, make it configurable.
Detect, remove and warn about null tile entities.
Spigot > Surge
Tick loop optimization - sleep for as long as possible.

Conflicts:
	src/main/java/net/minecraft/server/MinecraftServer.java
	src/main/java/org/bukkit/craftbukkit/command/TicksPerSecondCommand.java