flag_set iterator(s) and/or for_each(flag_set<E>, [](E){})

[ehoeks]

As many programmers I sometimes need to do some work for all flags set in an flag_set.

Can we add an type_safe way to iterate over all 'set' flags in an flag_set?
e.g.

enum class my_enum; // some flag_set compatible enum class

void do_something_with(my_enum e);

{
  type_safe::flag_set<my_enum> some_flag_set();

  type_safe::for_each(
    some_flag_set,
    [](f){ do_something_with(f); }
  );
}

[foonathan]

If you be willing to write something, I'm happy for a PR.

[NikolausDemmel]

In case someone works on this, I think range syntax would also be nice:

  for (auto f : some_flag_set) {
    do_something_with(f);
  }