Update some meta

Including some explanation of the YAML command, and a forgotten arg in
the health command (Related commit for health coming soon)
Also a apparently the "item" context wasn't actually being added in that
event.
Improve Health command functionality

It now will automatically add the health trait to NPCs when needed
add element.upper/lower

Quick tags to adjust the casing of elements
Add Player Jump smartevent

A simple event that was requested to fire when a player jumps into the
air.
Using smart event instead of a normal world event because onPlayerMove
tends to fire very very often, and players jump fairly often... better
to minimize need for this.
There is no proper Bukkit event (thus the player move with weird 'if'
logic)
Cannot really properly block the jump either, so no 'determine
cancelled' is possible for now.
Future possibility ( @aufdemrand ) is 'on player jumps in <notable
cuboid>' or something. Would like to see definite stability in said
system + fully working cuboid-related events before going for it though.
Simplify some world script meta

Just some meta that I noticed had way too many variations... probably a
lot more like this, just the first of many Event meta updates to come...
Merge pull request #548 from mcmonkey4eva/master

Pull all the requests