* New method ConfigVarList.extend to create variables from a dictionary of values.
* ConfigVarList can be initialized with a dictionary of values.
* ConfigVarStack can resolve $(A<B:b, C:c>) style varaibles.
* New variable syntax  $(A<B:b, C:c>)  to allow "scoped" resolving. This is similiar to function calls.
* New interactive command: resolvel calls resolve_to_list.