Implements keyboard accessibility, as requested by @mattmachel in issue #2, with the following features:
Carousels will respond to up and down on vertically scrolling carousels, left and right on horizontally scrolling carousels and all four directions on class-only carousels.
Carousels with focus will prevent scrolling the page in the browser - this is by design.
Carousels with focus will prevent automatic cycling through the carousel items.
Implements keyboard accessibility, as requested by @mattmachel in issue #2, with the following features: