fix dangling references and clean up dates

index does not need to be listed in the table of contents -- everyone
would get there first before they find this table anyhow.

and the link from background.rst to the "features" document was broken by
d61d4f3 (which renamed it to
"principles") and then again by
1b359e6 (which merged "principles"
directly into background.rst in the first place.

I use this opportunity to clean up the dates included here as well.

doc/background.rst

@@ -40,28 +40,29 @@ how you may talk with us and who "we" are currently.
 
 
 The Technical Autocrypt Approach
---------------------------------------
+--------------------------------
 
 Autocrypt uses regular E-Mail messages between people to piggyback
 necessary information to allow encrypting subsequent messages; it adds
 a new :mailheader:`Autocrypt` E-Mail header for transferring public
 keys and driving encryption behaviour. By default, key management is
-not visible to users. See :doc:`features` for more technical and UI
-cornerstones.
+not visible to users. See below for more details about the differences
+from other attempts at providing encrypted e-mail.
 
 We are following this approach step-by-step using different "Levels"
 of implementation compliance.  Driven by usability concerns, we are
 refining and implementing :doc:`Level 1 <level1>` in several mail apps
-during summer 2017, aiming for a release party during autumn 2017 which
-marks the first `real-life implementation milestone <https://github.com/autocrypt/autocrypt/milestone/1>`_.
-If you are interested to learn more or want to help please :doc:`join our channels and look at
-where we meet next <contact>`.
+during 2017, aiming for a release at the end of 2017 which marks the
+first `real-life implementation milestone
+<https://github.com/autocrypt/autocrypt/milestone/1>`_.  If you are
+interested to learn more or want to help please :doc:`join our
+channels and look at where we meet next <contact>`.
 
 See :doc:`contents` for an index of all docs and discussion results so far.
 
 
-Design Differences To Previous Approaches
------------------------------------------
+Design Differences From Previous Approaches
+-------------------------------------------
 
 End-to-end encrypted e-mail has been around for decades, but has failed
 to see wide adoption outside of specialist communities, in large part

doc/contents.rst

@@ -5,10 +5,6 @@ Current docs (work-in-progress)
 The following in-progress documents are written for early adopters
 and contributors, MUA developers and privacy enthusiasts.
 
-:doc:`index`
-     introduction to why Autocrypt exists and why it is trying
-     to achieve more e-mail encryption.
-
 :doc:`background`
      discusses the motiviation, technical, social and design
      approaches of Autocrypt.