Files:
   asum.ys: Y86 code for a function that sums the elements
      of an array of integers. Nothing but standard y86
	  instructions here.

   asum-inc.ys: A modified version that uses the incl instruction.
      won't work unless the simulator supports incl.

   asum_r.ys: Yet another version, this one uses a recursive
      function to sum the array. This give the leave instruction
      a workout (won't work unless the simultor supports leave
	  correctly).

   pow.ys: computes powers of two using the dbl instruction.
      Won't work unless the simulator supports dbl.