def mount(app, options)
      mounted[app] = App.new(app, options.fetch(:at))
    end
def mount(app, options)
      mounted[app] = App.new(app, options.fetch(:at))
    end
@api private
 Mount a Hanami::Application or a Rack app

 @param app [#call] an application compatible with Rack SPEC
 @param options [Hash] a set of options
 @option :at [String] options the mount point

 @since 0.9.0

 @example
   # config/environment.rb
   # ...
   Hanami.configure do
     mount Web::Application, at: '/'

     # ...
   end