Added the possibility to change colors

For my project i needed a darker background so i added the possibility to change the color not only for the background but also for the title and for the details.

Now you can do something like that:

ShowcaseView.ConfigOptions co = new ShowcaseView.ConfigOptions();
co.titleTextColor=something;
ShowcaseView.insertShowcaseView(R.id.btn, this, "title", "details,", co);

and it's done.