Create abstract class for exponential
Create a exponential_abst_t
abstract class and make the electronic exponential_t
an extension of this class. The electronic exponential_t
type should be renamed to exponential_elec_t
in preparation for the addition of new types of systems.
For the moment the abstract class should be quite minimal and we should only add things to it as they become necessary.
Edited by Micael Oliveira