Add linestyle option for plot_multiple

Sometimes one may wish to use linestyles as well as colors to differentiate results plotted together with plot_multiple. This merge request adds that functionality.

In the process, I found that hist_kwargs and label_kwargs would not update properly in plot_corner, overwriting defaults instead of updating them. This MR now fixes that issue as well.

bilby/core/result.py

@@ -1177,22 +1177,34 @@ class Result(object):
         if utils.command_line_args.bilby_test_mode:
             return
 
-        # bilby default corner kwargs. Overwritten by anything passed to kwargs
         defaults_kwargs = dict(
-            bins=50, smooth=0.9, label_kwargs=dict(fontsize=16),
+            bins=50, smooth=0.9,
             title_kwargs=dict(fontsize=16), color='#0072C1',
             truth_color='tab:orange', quantiles=[0.16, 0.84],
             levels=(1 - np.exp(-0.5), 1 - np.exp(-2), 1 - np.exp(-9 / 2.)),
             plot_density=False, plot_datapoints=True, fill_contours=True,
-            max_n_ticks=3, hist_kwargs=dict(density=True))
+            max_n_ticks=3)
 
         if 'lionize' in kwargs and kwargs['lionize'] is True:
             defaults_kwargs['truth_color'] = 'tab:blue'
             defaults_kwargs['color'] = '#FF8C00'
 
+
+        label_kwargs_defaults = dict(fontsize=16)
+        hist_kwargs_defaults = dict(density=True)
+
+        label_kwargs_input = kwargs.get("label_kwargs", dict())
+        hist_kwargs_input = kwargs.get("hist_kwargs", dict())
+
+        label_kwargs_defaults.update(label_kwargs_input)
+        hist_kwargs_defaults.update(hist_kwargs_input)
+
         defaults_kwargs.update(kwargs)
         kwargs = defaults_kwargs
 
+        kwargs["label_kwargs"] = label_kwargs_defaults
+        kwargs["hist_kwargs"] = hist_kwargs_defaults
+
         # Handle if truths was passed in
         if 'truth' in kwargs:
             kwargs['truths'] = kwargs.pop('truth')
@@ -2029,6 +2041,7 @@ def plot_multiple(results, filename=None, labels=None, colours=None,
         hist_kwargs = kwargs.get('hist_kwargs', dict())
         hist_kwargs['color'] = c
         hist_kwargs["linestyle"] = linestyle
+        kwargs["hist_kwargs"] = hist_kwargs
         fig = result.plot_corner(fig=fig, save=False, color=c, contour_kwargs={"linestyle":linestyle}, **kwargs)
         default_filename += '_{}'.format(result.label)
         lines.append(mpllines.Line2D([0], [0], color=c, linestyle=linestyle))