Fix HTTP links in URI docs.

lib/dartdoc/markdown.dart

Index: lib/dartdoc/markdown.dart
diff --git a/lib/dartdoc/markdown.dart b/lib/dartdoc/markdown.dart
index b0a177cc483583c39e548cf9317960512bdb0791..02c099f5a7ba1e3ac0fe647b843d5ea01bceaf68 100644
--- a/lib/dartdoc/markdown.dart
+++ b/lib/dartdoc/markdown.dart
@@ -57,8 +57,8 @@ class Document {
       final match = pattern.firstMatch(lines[i]);
       if (match != null) {
         // Parse the link.
-        final id = match[1];
-        final url = match[2];
+        var id = match[1];
+        var url = match[2];
         var title = match[3];
 
         if (title == '') {
@@ -69,6 +69,9 @@ class Document {
           title = title.substring(1, title.length - 1);
         }
 
+        // References are case-insensitive.
+        id = id.toLowerCase();
+
         refLinks[id] = new Link(id, url, title);
 
         // Remove it from the output. We replace it with a blank line which will