Added Showcase Sequence Helper

[jbc25]

To facilitate create many showcase screens. Example:

    ```

ShowcaseSequenceHelper.newInstace(this) .addNewShowcase(ID_SHOWCASE_HOT_NUMBERS, new ViewTarget(recyclerHot), getString(R.string.hot_numbers_showcase_title), getString(R.string.hot_numbers_showcase_detail))

            .addNewShowcase(ID_SHOWCASE_HISTORY_ICON,
                    new ToolbarActionItemTarget(getToolbar(), R.id.menu_history),
                    getString(R.string.hot_numbers_showcase_title),
                    getString(R.string.hot_numbers_showcase_detail))

            .show();

[insearching]

Hi, could you please add this to Readme?

[Susiew78]

Ok i will