Add read/write functions for optimizer
During learning curve analysis it is rather common to store the results of an optimization (i.e. the
While many of the key objects in hiphive (and icet) have read/write functionality, the
Optimizer class does not.
As a result, one is forced to resort to pickle manuallt, which has various disadvantages.
Therefore, we should consider adding read/write methods (possibly internally based on pickle, although that would create potential problems between versions).