exterminator scenario (#2126)

```
scripts/play.sh --scenario data/scenarios/Challenges/Ranching/pied-piper.yaml --autoplay
```

In addition to the scenario, this PR:
1. Adds support for colorizing robot names
2. Improves diagnostic message for subworld portal spatial consistency enforcement

data/scenarios/Challenges/Ranching/00-ORDER.txt

@@ -3,3 +3,4 @@ capture.yaml
 powerset.yaml
 fishing.yaml
 gated-paddock.yaml
+pied-piper.yaml

data/scenarios/Challenges/Ranching/_pied-piper/rat.sw

@@ -0,0 +1,107 @@
+def moveWithMorbidity =
+    moldHere <- ishere "mold";
+    if moldHere {
+        try {
+            // handle race conditions in which
+            // another robot grabs it first
+            m <- harvest;
+            let spores = "mold spores" in
+            if (m == spores) {
+                say $ "Yuck, " ++ spores ++ "! I'm outta here.";
+                selfdestruct;
+            } {};
+        } {};
+    } {};
+    move;
+    end;
+
+def goFoodDir = \f. \r.
+    let d = fst r in
+    if (d == down) {
+        foodHere <- ishere "oats";
+        if foodHere {
+            grab; return ()
+        } {};
+        f;
+        return ()
+    } {
+        turn d;
+
+        // An obstruction might arise after
+        // navigation direction is determined
+        // but before we move.
+        try {
+            moveWithMorbidity;
+        } {};
+        f;
+    }
+    end;
+
+def goHomeDir = \f. \r.
+    let d = fst r in
+    if (d == down) {
+        return ()
+    } {
+        turn d;
+
+        // An obstruction might arise after
+        // navigation direction is determined
+        // but before we move.
+        try {
+            moveWithMorbidity;
+        } {};
+        f;
+    }
+    end;
+
+def findGoodDirection =
+    isBlocked <- blocked;
+    if isBlocked {
+        turn left;
+        findGoodDirection;
+    } {};
+    end;
+
+def moveUntilBlocked =
+    isBlocked <- blocked;
+    if isBlocked {
+    } {
+        moveWithMorbidity;
+        moveUntilBlocked;
+    };
+    end;
+
+def pauseAtRandom =
+    r <- random 3;
+    if (r == 0) {
+        r2 <- random 12;
+        wait $ 6 + r2;
+    } {}
+    end;
+
+def returnHome = \homeLoc.
+    nextDir <- path (inL ()) (inL homeLoc);
+    case nextDir return $ goHomeDir $ returnHome homeLoc;
+    end;
+
+def pursueFood = \hadSensedFood. \homeLoc.
+    nextDir <- path (inR 5) (inR "oats");
+    case nextDir (\_. if hadSensedFood {returnHome homeLoc} {return ()}) $
+        goFoodDir $ pursueFood true homeLoc;
+    end;
+
+def doMovement = \startLoc.
+    findGoodDirection;
+    moveUntilBlocked;
+    pauseAtRandom;
+    pursueFood false startLoc;
+    end;
+
+/** Loop */
+def go = \startLoc.
+    doMovement startLoc;
+    go startLoc;
+    end;
+
+startLoc <- whereami;
+go startLoc;

data/scenarios/Challenges/Ranching/_pied-piper/solution.sw

@@ -0,0 +1,191 @@
+def doN = \n. \f. if (n > 0) {f; doN (n - 1) f} {}; end;
+
+
+def intersperse = \n. \f2. \f1. if (n > 0) {
+        f1;
+        if (n > 1) {
+            f2;
+        } {};
+        intersperse (n - 1) f2 f1;
+    } {};
+    end;
+
+def uTurn = \d.
+    turn d;
+    move;
+    turn d;
+    end;
+
+/**
+Starting at bottom right of field
+*/
+def harvestField = \fieldWidth.
+    intersperse fieldWidth move harvest;
+    uTurn right;
+    intersperse fieldWidth move harvest;
+    uTurn left;
+    intersperse fieldWidth move harvest;
+    uTurn right;
+    intersperse fieldWidth move harvest;
+    end;
+
+def makeOatsCrumb = \spacing.
+  place "oats";
+  doN spacing move;
+  end;
+
+def waitUntilRatDisappeared =
+  found <- scout east;
+  if found {
+      wait 1;
+      waitUntilRatDisappeared;
+  } {};
+  end;
+
+/**
+Place a trail of breadcrumbs, and return
+one crumb short of the first crumb.
+*/
+def makeOatsTrail = \spacing. \segments.
+  doN segments $ makeOatsCrumb spacing;
+  turn back;
+  doN (segments * spacing) move;
+  turn back;
+  end;
+
+def placeHorizontalTrail = \horizontalSpacing.
+  turn east;
+  doN (2*horizontalSpacing) move;
+  place "oats";
+  turn back;
+  doN horizontalSpacing move;
+  place "oats";
+  doN horizontalSpacing move;
+  turn left;
+  end;
+
+def waitForRatToPass =
+
+  // Wait until the rat ate this crumb
+  watch down;
+  wait 2000;
+  waitUntilRatDisappeared;
+  end;
+
+def makeTrails =
+  let spacing = 4 in
+  let segments = 5 in
+
+  wait 30;
+  placeHorizontalTrail 5;
+  makeOatsTrail spacing $ segments + 1;
+  end;
+
+def getKey =
+  turn east;
+  doN 15 move;
+  turn right;
+  move;
+  _k <- grab;
+  turn right;
+  doN 5 move;
+  turn right;
+  doN 6 move;
+  turn left;
+  doN 18 move;
+  turn left;
+  doN 20 move;
+  turn right;
+  doN 2 move;
+  use "unlocker" forward;
+  doN 6 move;
+  turn right;
+  doN 8 move;
+  turn left;
+  move;
+  turn right;
+  doN 6 move;
+  turn left;
+  move;
+  end;
+
+def placeMold = \moldItem.
+  turn east;
+  doN 11 move;
+  sow moldItem;
+  end;
+
+def go =
+  getKey;
+  harvestField 20;
+
+  turn left;
+  doN 2 move;
+  turn left;
+  harvestField 20;
+
+
+  move;
+  turn right;
+  doN 14 move;
+  turn left;
+
+  // Get the mold
+  doN 4 move;
+  turn left;
+  doN 3 move;
+  moldItem <- grab;
+  turn back;
+  doN 3 move;
+
+  turn right;
+  doN 3 move;
+  turn left;
+
+  // Head back to the house
+  doN 8 move;
+  turn left;
+  doN 8 move;
+  turn left;
+
+  // Start laying trail
+  intersperse 5 (doN 4 move) $ place "oats";
+  placeHorizontalTrail 5;
+
+  waitForRatToPass;
+
+  makeTrails;
+  waitForRatToPass;
+
+
+  makeOatsTrail 4 10;
+  placeHorizontalTrail 5;
+  waitForRatToPass;
+
+  makeOatsTrail 4 12;
+  placeHorizontalTrail 5;
+  waitForRatToPass;
+
+  turn east;
+  doN 2 move;
+
+  placeHorizontalTrail 4;
+  makeOatsTrail 4 4;
+  waitForRatToPass;
+
+  makeOatsTrail 4 6;
+  placeHorizontalTrail 4;
+
+  waitForRatToPass;
+  makeOatsTrail 4 10;
+  placeHorizontalTrail 4;
+
+
+  waitForRatToPass;
+  makeOatsTrail 4 12;
+  placeHorizontalTrail 4;
+
+  placeMold moldItem;
+  end;
+
+go;