Mod.  Implement shutdown logic in `close()`.  Since this class is singleton an external call to a reference will not remove the internal __instance representation and hence not call the destructor.
Add. namedtuple varMapping to define mapping from query variables to metric variables more clearly.
Mod.  In process_metrics() use the mediator to map var names.
Mod. REQUEST_META_QUERY_STR stores all potential query variables.  Added new values.
Mod.  RequestMetaFactory() to dynamiclly build a RequestMeta type based on the definition of metric parameters.  Fixed other references to RequestMeta objects to ensure the proper interface is tested for.