plot_utils: teach pre_plot_setup() setup multirow plots
diff --git a/cr2/plot_utils.py b/cr2/plot_utils.py
index f803f4f..874f516 100644
--- a/cr2/plot_utils.py
+++ b/cr2/plot_utils.py
@@ -50,7 +50,7 @@
     """
     set_lim(ylim, ax.get_ylim, ax.set_ylim)
 
-def pre_plot_setup(width=None, height=None, ncols=1):
+def pre_plot_setup(width=None, height=None, ncols=1, nrows=1):
     """initialize a figure
 
     width and height are numbers.  This function should be called
@@ -68,7 +68,7 @@
         if width is None:
             width = height * GOLDEN_RATIO
 
-    _, axis = plt.subplots(ncols=ncols, figsize=(width, height))
+    _, axis = plt.subplots(ncols=ncols, nrows=nrows, figsize=(width, height))
 
     return axis