This makes more sense, because "generate" implies *running*
a generator, not *returning* from a generator. That name was
a vestige of the time when libfringe only really provided a .next()
implementation, which made marginally more sense together with
.generate(), but it doesn't anymore when we have .resume().
The new design concerns itself with one thing and exactly one thing:
passing values back and forth with an extern "C" function.
This allows to simplify fringe::arch into a single primitive, swap.
Close#21
