ShowcaseViews for showing guides one after another

[darekdeo]

Hi, I've made this wrapper like 1 year ago when I needed to show multiple showcase views one after another.

Forgot to put it on git earlier, It's small addition to library, hope it will be useful for someone else too.

If you decide to pull it, feel free to make any changes.

[darekdeo]

Just don't merge readme.md, I've changed that file too. Basicly wrapper is only one class "ShowcaseViews".

There are few things to edit/fix/consider:

1. Optional enable/disable views setting doesn't work great, I think it should rather save state of view before disabling it. Currently if user decides to call setDisableViewGroup(), all views will be enabled after showcase ends. I think it should bring back earlier state of views instead.
2. Method names, like to use build() instead of show(). ;)
3. 3rd listener callback whenever next view is shown with id of the view.