cameo: new command "stats" to print path statistics

- README: documented the "stats" command
- lang.l, lang.y: added "stats" command
- path.h (path_stats), path.c (path_stats): calculate and print path
  statistics

cameo/path.c

@@ -406,3 +406,25 @@ again:
 		}
 	return path;
 }
+
+
+void path_stats(const struct path *path)
+{
+	int paths = 0, segs = 0;
+	double len = 0;
+	const struct point *p;
+
+	while (path) {
+		paths++;
+		for (p = path->first; p; p = p->next) {
+			if (!p->next)
+				continue;
+			segs++;
+			len += hypot(hypot(p->x-p->next->x, p->y-p->next->y),
+			    p->z-p->next->z);
+		}
+		path = path->next;
+	}
+	fprintf(stderr, "%d path%s, %d segment%s, %f mm\n",
+	    paths, paths == 1 ? "" : "s", segs, segs == 1 ? "" : "s", len);
+}