Implementing STL iterators are a bloody PITA

You don't need iterators for the range-based for loop, just a .begin() and .end() method which returns a raw pointer is enough.

E.g.:

https://github.com/floooh/oryol/blob/eb08cffe1b1cb6b05ed14ec...

(don't use that project though because it's been archived, I've switched back to plain old C in the meantime)