Improve the document structure in several places

Change-Id: Icea6d0b0d9628eb171f5673b397f1db7f1c5c5b8
diff --git a/index.rst b/index.rst
index e3346ab..3dff38e 100644
--- a/index.rst
+++ b/index.rst
@@ -1,25 +1,16 @@
-
 NDN Packet Format Specification
 ===============================
 
-
 .. toctree::
+   :maxdepth: 3
+
    intro
    tlv
    name
    interest
    data
    signature
-   link
    signed-interest
+   link
    types
    changelog
-   :maxdepth: 3
-
-
-.. Indices and tables
-.. ==================
-
-.. * :ref:`genindex`
-.. * :ref:`modindex`
-.. * :ref:`search`