Revise changelog sections likely to be mangled by formatter script

  o Major features (directory mirrors):

    - Include an opt-in trial list of Default Fallback Directories in

      add_default_fallback_dir_servers().

      "Tor has included a feature to fetch the initial consensus from nodes

       other than the authorities for a while now. We just haven't shipped a

       list of alternate locations for clients to go to yet.

       Reasons why we might want to ship tor with a list of additional places

       where clients can find the consensus is that it makes authority

       reachability and BW less important.

       We want them to have been around and using their current key, address,

       and port for a while now (120 days), and have been running, a guard,

       and a v2 directory mirror for most of that time."

      We exclude BadExits and tor versions that aren't recommended.

      We include an IPv6 address for each FallbackDir (see ticket 8374).

      (Tor might not use IPv6 fallbacks until ticket the code for ticket6027 is merged.)

      The unit test ensures that we successfully load all included

      default fallback directories.

      add_default_fallback_dir_servers().  Doing this should improve

      client reliability and initial bootstrap performance, and reduce

      load on the directory authorities.

      Closes ticket 15775. Patch by "teor".

      OnionOO script by "weasel", "teor", "gsathya", and "karsten".

      672 bytes per circuit.  Closes ticket 17796.

  o Minor features (directory system):

    Previously only relays who explicitly opened a directory port (DirPort)

    - Previously only relays who explicitly opened a directory port (DirPort)

      accepted directory requests from clients.  Now all relays, with and without

      a DirPort, who do not disable the DirCache option accept and serve

      directory requests sent (tunnelled) through their ORPort.