Add milti-line title

Author: hannahker

test/image/mocks/zzz-automargin-title-paper-multiline.json

@@ -0,0 +1,28 @@
+{
+    "data": [
+        {
+            "showlegend": false,
+            "type": "scatter",
+            "x": [
+            1,
+            2,
+            3
+            ],
+            "y": [
+            4,
+            5,
+            6
+            ]
+        }],
+    "layout": {
+        "height": 300,
+        "width": 400,
+        "margin": {"t":0, "b": 0, "l": 0, "r": 0},
+        "title": {
+            "automargin": true, 
+            "text": "Paper<br>Multi-line",
+            "pad": {"t": 0, "b": 0},
+            "yref": "paper"
+        }
+  }
+}