Moved some common logic in Carousel to a mixin.
Added a Fader component.
Updated the README to cover Fader.
Removed noop import in Fader.

See
https://github.com/jussi-kalliokoski/merry-go-round/pull/7/files#r21369500.
Renamed a function per review.
Replaced true/false assertions with equal(true|false), per review.
Merge pull request #7 from jussi-kalliokoski/fader

New Fader component