def to_json( *args )
      h = to_hash( *args )
      a = []
      s = StringIO.new

      s.print "{ "
      h.each_pair do |k,v|
        a << "\"#{k}\": #{v}"
      end
      s.print a.join(", ")
      s.print "}"
      return s.string
    end
def to_json( *args )
      h = to_hash( *args )
      a = []
      s = StringIO.new

      s.print "{ "
      h.each_pair do |k,v|
        a << "\"#{k}\": #{v}"
      end
      s.print a.join(", ")
      s.print "}"
      return s.string
    end
call-seq:
   stat.to_json  -> String
   stat.to_json( *args ) -> String

 return a json string of the stats.  By default this returns a json string
 of all the stats.  If an array of items is passed in, those that match the
 known stats will be all that is included in the json output.