Merge pull request #2847 from Jacalz/remove-all-slow

Add docs for container.Remove() when removing everything

container.go

@@ -139,6 +139,8 @@ func (c *Container) Refresh() {
 }
 
 // Remove updates the contents of this container to no longer include the specified object.
+// This method is not intended to be used inside a loop, to remove all the elements.
+// It is much more efficient to just set .Objects to nil instead.
 func (c *Container) Remove(rem CanvasObject) {
 	if len(c.Objects) == 0 {
 		return