cstruct.iter vs cstruct.fold

[mor1]

currently, Cstruct.iter basically turns a buffer in to an iterable of parsed structures. Cstruct.fold then folds over such an iterable with an accumulator.

it seems like there should also be functions that iterate and map over the iterable that comes out of Cstruct.iter, and (perhaps) that the current Cstruct.iter should be renamed to Cstruct.mk_iter or somesuch.

thoughts?