Add group reporting

Still needs some testing, so the option isn't documented yet. The
standard deviation averaging also isn't mathematically sound.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/io_u.c b/io_u.c
index 5b5802c..79a0ce8 100644
--- a/io_u.c
+++ b/io_u.c
@@ -286,8 +286,8 @@
 		break;
 	}
 
-	td->ts->io_u_map[index]++;
-	td->ts->total_io_u++;
+	td->ts.io_u_map[index]++;
+	td->ts.total_io_u++;
 }
 
 static void io_u_mark_latency(struct thread_data *td, unsigned long msec)
@@ -321,7 +321,7 @@
 		break;
 	}
 
-	td->ts->io_u_lat[index]++;
+	td->ts.io_u_lat[index]++;
 }
 
 /*