clogger 2.0.1 - doc updates and new mailing list

Most notably, there's a new mailing list at

    clogger-public@bogomips.org

You may (optionally) subscribe to the new mailing list at:

    clogger-public+subscribe@bogomips.org

If you're on librelist, you'll need to subscribe manually since
librelist subscribers cannot be imported.  Of course, you do not
have to be subscribed to post, either (please Cc: everyone as folks
may not be subscribed).

shortlog:
      README: document $env support for reading Rack env
      switch docs + website to olddoc
      ext: get rid of noisy and unnecessary cast
      new mailing list at clogger-public@bogomips.org
      gemspec: use SPDX license abbreviation
      remove Rubyforge reference in Rakefile