Improve the wrapper markup

[jasonwebb]

• Add role="region" to the outermost wrapper.
• Add a generic but clear aria-label to the wrapper.
  • Consider using "carousel" as the default.
• Consider making the aria-label configurable with a new setting.
  • This should come with some guidance about what makes an aria-label effect in this use case.

[jasonwebb]

In 3c74fc6, a new setting is now available: regionLabel. Use it to provide custom text to use as the aria-label value on the wrapper (default is 'carousel').

This setting can also be defined through the data attribute data-regionlabel placed on the wrapper element used to initialize the Slick package.

Additional documentation is available in the main README in the New features and New settings sections.