Add a script to generate HTML and DOM docs with cross-links to one another.

frog/library.dart

Index: frog/library.dart
diff --git a/frog/library.dart b/frog/library.dart
index 2bf79ebfb8521f1f8ae622986e33891b12517e4c..aed4b437fcee3b89e47dab1d0436da26ddd651da 100644
--- a/frog/library.dart
+++ b/frog/library.dart
@@ -283,6 +283,11 @@ class Library extends Element {
   }
 
   toString() => baseSource.filename;
+
+  int hashCode() => baseSource.filename.hashCode();
+
+  bool operator ==(other) => other is Library &&
+    other.baseSource.filename == baseSource.filename;
 }