Should the args iterator be divided into iter_args/iter_kwargs instead?

[bayerj]

The construction of different arguments for each iteration of the optimizer is somehow tedious. However, in the case of some optimizers (HF, KSD) there are several arguments. E.g., KSD needs a different argument iterator for the gradient calcuation, the subspace construction and the inner loop. If that would result in 6 different arguments passed to the constructor, that'd be rather ugly.

Needs more thought.