ocaml: phase 5.1 prime_factors.ml baseline (trial-division, 360 factor sum = 17)

Three refs threading through a while loop:
  m       remaining quotient
  d       current divisor
  result  accumulator (built in reverse, List.rev at end)

  while !m > 1 do
    if !m mod !d = 0 then begin
      result := !d :: !result;
      m := !m / !d
    end else
      d := !d + 1
  done

360 = 2^3 * 3^2 * 5 factors to [2;2;2;3;3;5], sum 17.

60 baseline programs total — milestone.

lib/ocaml/baseline/expected.json

@@ -46,6 +46,7 @@
   "pi_leibniz.ml": 314,
   "pretty_table.ml": 64,
   "poly_stack.ml": 5,
+  "prime_factors.ml": 17,
   "queens.ml": 2,
   "quicksort.ml": 44,
   "roman.ml": 44,