Try a different colorization of printArtifactPretty output in README

Author: Mikolaj

README.md

@@ -88,15 +88,15 @@ The vector-Jacobian product program (presented below with additional formatting)
 
 ```hs
 >>> printArtifactPretty artifact
-"\dret m1 ->
-   let m3 = sin (tproject2 (tproject1 m1))
-       m4 = tproject1 (tproject1 m1) * m3
-       m5 = recip (tproject2 m1 * tproject2 m1 + m4 * m4)
-       m7 = (negate (tproject2 m1) * m5) * dret + tproject2 m1 * dret
-    in tpair
-         (tpair (m3 * m7)
-                (cos (tproject2 (tproject1 m1)) * (tproject1 (tproject1 m1) * m7)))
-         ((m4 * m5) * dret + m4 * dret)"
+\dret m1 ->
+  let m3 = sin (tproject2 (tproject1 m1))
+      m4 = tproject1 (tproject1 m1) * m3
+      m5 = recip (tproject2 m1 * tproject2 m1 + m4 * m4)
+      m7 = (negate (tproject2 m1) * m5) * dret + tproject2 m1 * dret
+  in tpair
+       (tpair (m3 * m7)
+              (cos (tproject2 (tproject1 m1)) * (tproject1 (tproject1 m1) * m7)))
+       ((m4 * m5) * dret + m4 * dret)
 ```
 
 A concrete value of this symbolic reverse derivative at the same input as before can be obtained by interpreting its program in the context of the operations supplied by the horde-ad library. (Note that the output happens to be the same as `gradSumFooMatrix threeSimpleMatrices` above, which used `cgrad` on `kfromS . ssum0 . foo`; the reason is that `srepl 1.0` happens to be the reverse derivative of `kfromS . ssum0`.)