Variables by module and as an object

Process all the variables as one for a module to improve performance for modules with a lot of variables. Process them as an object to help organise the variables for the module and create an effective namespace.

I created a module for D7, http://petermoulding.com/variable_module, to add the OO approach on top of the current get/set/del functions. The approach could easily be implemented with the object behind the current functions for a transitional period in Drupal 8 then the current functions could be dropped in Drupal 9.