Updated markdown library. This adds support for images in the doccumentation!

third_party/pkg/markdown/lib/src/util.dart

 library markdown.util;
 
 /// Replaces `<`, `&`, and `>`, with their HTML entity equivalents.
 String escapeHtml(String html) {
+  if (html == '' || html == null) return null;
   return html.replaceAll('&', '&amp;')
              .replaceAll('<', '&lt;')
              .replaceAll('>', '&gt;');
 }
+
+/// Removes null or empty values from [map].
+void cleanMap(Map map) {
+  map.keys
+    .where((e) => isNullOrEmpty(map[e]))
+    .toList()
+    .forEach(map.remove);
+}
+
+/// Returns true if an object is null or an empty string.
+bool isNullOrEmpty(object) {
+  return object == null || object == '';
+}