add unit tests for Carousel slid events
README: Authors => Creators
Add direction & relatedTarget properties to slid.bs.carousel event
Fixes #13393
Document .direction & .relatedTarget properties of Carousel events.
Fixes #13395
Merge pull request #13414 from twbs/readme-tweak

README: Authors => Creators
fix #13427
change 'slid' comments per @fat's feedback
Carousel.slide: rename e => slideEvent
Merge pull request #13396 from twbs/carousel-events

Carousel event properties
Update JSZip to v2.2.1.
Update holder.js to v2.3.2.
Run `grunt`.