chore(classes): Catch and deprecate old inheritance from new classes

classes/base.lua

@@ -182,6 +182,18 @@ local base = pl.class({
     options = {},
 
     _init = function (self, options)
+      if options.id then
+        -- The old std.object inheritence for classes called the base class with
+        -- and arg of a table which had an ID. Since the new system doesn't have
+        -- an ID arg, we can assume this is unported code. See also core/sile.lua
+        -- for deprecation system for the old SILE.baseClass.
+        SU.warn([[
+        The inheritance system for SILE classes has been refactored using a
+          different object model, please update your code as use of the old
+          model will cause unexpected errors and will eventually be removed.
+        ]])
+        SU.deprecated("std.object x", "pl.class", "0.10.10", "0.12.0")
+      end
       if not options then options = {} end
       self:declareOption("class", function (name) return name end)
       self:declareOption("papersize", function (size)