add window_class method

[rdp]

Since I'm a bit lazy...

module RAutomation
  module Adapter
    module WinFfi
      class Window
        def class_name
          Functions.window_class(hwnd)
        end
      end
    end
  end
end

[jarmo]

Added Window#class_names method instead which returns an Array of window and it's controls class names.

https://github.com/jarmo/RAutomation/commit/c110b9fe157e8b7b5a2c09c53c69a8f1693e0698