hud.register(name, def)
	-- name: statbar name (health, air, hunger, armor already used by default)
	-- def: <HUD item definition> (see below)

hud.change_item(player, name, def)
	-- player: player object
	-- name: statbar name
	-- def: table containing new values
		-- currently supported: number, text and offset

hud.swap_statbar(player, name1, name2) -- swaps position and offset of statbar with name1 with statbar with name2
	-- player: player object
	-- name1: statbar name
	-- name2: statbar name

hud.remove_item(player, name)

HUD item definition
{
	hud_elem_type = "statbar",		-- currently only supported type (same as in lua-api.txt)
	position = {x=<x>, y=<y>},		-- position of statbar (same as in lua-api.txt)
	size = {x=24, y=24},			-- statbar texture size (default 24x24), needed to be scaled correctly
	text = "hud_heart_fg.png",		-- texture name (same as in lua-api.txt)
	number = 20,				-- number/2 = number of full textures(e.g. hearts)
	max = 20,				-- used to prevent "overflow" of statbars
	alignment = {x=-1,y=-1},		-- alignment on screen (same as in lua-api.txt)
	offset = HUD_HEALTH_OFFSET,
	background = "hud_heart_bg.png",	-- statbar background texture name
	autohide_bg = false,			-- hide statbar background textures when number = 0
	events = {				-- called on events "damage" and "breath_changed" of players
		 {
			type = "damage",
			func = function(player)
				-- do something here
			end
		 }
	},
}
