allow insertion of custom middleware

BACKLOG

-------

- password protection

- enable websockets in ha

- gauge-view: interval selection dropdown 

- report: print number of samples, interval-size on topright via scalaexp-buttonstyle

  def initialized

    server = @opts[:server].downcase

    middleware_stack = @opts[:use]

    websocket = FnordMetric::WebSocket.new

    webapp    = FnordMetric::App.new(@opts)

      use Rack::CommonLogger

      use Rack::ShowExceptions

      map("/stream"){ run websocket }

      map("/"){ run webapp }

      map "/stream" do

        run websocket

      end

      map "/" do

        middleware_stack.each do |middleware| 

          use(*middleware[0..1], &middleware[2])

        end

        run webapp

      end

    end

    unless ["thin", "hatetepe"].include? server