= New Features

* A middleware_stack plugin has been added for more detailed control
  over middleware, allowing for the removal of middleware and the
  insertion of middleware before existing middleware.  Example:

    plugin :middleware_stack

    # Remove csrf middleware
    middleware_stack.remove{|m, *args| m == Rack::Csrf}

    # Insert csrf middleware before logger middleware
    middleware_stack.before{|m, *args| m == Rack::CommonLogger}.
      use(Rack::Csrf, raise: true)

    # Insert csrf middleware after logger middleware
    middleware_stack.after{|m, *args| m == Rack::CommonLogger}.
      use(Rack::Csrf, raise: true)

= Other Improvements

* The head plugin now calls close on the response body if the body
  responds to close.  Previously an existing response body was
  just ignored.
