Replace internal iteration functions in std::either and std::result

[Kimundi]

Either and Result currently define a bunch of internal iteration functions.
Where applicable, those should be replaced by external iterators.

[bluss]

I'm working on it

[bluss]

Can't find any internal iteration functions in Either, will submit the result changes.

[bluss]

working on replacing some of the rest of the functions.. not internal iterators, but vector -> vector functions.