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
featuring 7ns inlineable context switches, no more separately-built
assembly objects, and a vastly nicer interface.
incontext/outcontext are no more, context switch calls now take a single
context structure, which functions as both.
everything now also functions without any heap allocations -- for the
context setup, only an FnOnce() value is necessary.