That was a silly idea for a silly abstraction, and it brought no improvement, only confusion. So, revert it.
Close #19
The exception to this is %eax is used not %edi on x86 because its caller-save
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