ecs: removed .entity in components, components do not need to be tables, pass entity as a new argument in several callbacks, remove System.methods, add System:callback, System:emit and System:reorder, add System.w, improve documentation

The component methods system was awkward and didn't give much benefit compared to just using methods on Systems. Plus now we really only have data in entities.

Since we don't have component methods, the callback system had to be replaced; I integrated it with the default System methods since it's a relatively common behavior.

ecs/children.can

@@ -7,43 +7,34 @@ return {
 	filter = true,
 	default = {
 		parent = nil, -- reference to parent entity, if any
-		-- ... list of children
+		-- ... list of children to add when the entity is added to the world
+		children = {}, -- [children]=true,children... map+list of children currently in the entity children (don't set this yourself)
 	},
-	methods = {
-		--- Add a new entity to the world, using this entity as a parent.
-		add = :(c, o)
-			if not o.children then
-				o.children = {}
-			end
-			o.children.parent = c.entity
-			table.insert(c, o)
-			@world:add(o)
-		end,
-		--- Remove an entity from the world and from this entity's children.
-		remove = :(c, o)
-			@world:remove(o)
-			for i=#c, 1, -1 do
-				if c[i] == o then
-					table.remove(c, i)
-					break
-				end
-			end
-			o.children.parent = nil
+	onAdd = :(c, e)
+		if c.parent then -- add to parent
+			let parentcc = c.parent.children.children
+			table.insert(parentcc, e)
+			parentcc[e] = true
 		end
-	},
-	onAdd = :(c)
-		for _, o in ipairs(c) do
-			o.children.parent = c.entity
+		for _, o in ipairs(c) do -- add children
+			if not o.children then o.children = {} end
+			o.children.parent = e
 			@world:add(o)
 		end
 	end,
-	onRemove = :(c)
-		for _, o in ipairs(c) do
-			@world:remove(o)
-			o.children.parent = nil
+	onRemove = :(c, e)
+		for i=#c.children, 1, -1 do -- remove children
+			@world:remove(c.children[i])
 		end
-		if c.parent then
-			c.parent.children:remove(c.entity)
+		if c.parent then -- remove from parent
+			let parentcc = c.parent.children.children
+			for i=#parentcc, 1, -1 do
+				if parentcc[i] == e then
+					table.remove(parentcc, i)
+					break
+				end
+			end
+			parentcc[e] = nil
 		end
 	end
 }