Add configuration to render line breaks as <br> or not

tests/lib/snapshots/markdown-test.js.md

@@ -73,4 +73,18 @@ Generated by [AVA](https://ava.li).
 > Snapshot 2
 
     `<p data-line="0">This is a &quot;QUOTE&quot;.</p>␊
+    
+
+## Markdown.render() should render line breaks correctly
+
+> Snapshot 1
+
+    `<p data-line="0">This is the first line.<br />␊
+    This is the second line.</p>␊
     `
+
+> Snapshot 2
+
+    `<p data-line="0">This is the first line.␊
+    This is the second line.</p>␊
+    `