1.0.28.75: documentation work related to move to Launchpad

* Delete SUPPORT and minimize BUGS.

  The information that used to be there is now the first chapter of
  the manual: "Getting Support and Reporting Bugs", Maybe it belongs
  elsewhere, but IMO it should be as prominent as we can make it - so
  the first chapter for now.

  Refer to Lauchpad and sbcl-bugs in "Reporting Bugs".

  Remove Dan B. from support providers for now, given that
  metacircles.com is currently domain-parked.