adjusted slider directions

[bennettatoms]

Hi, I really liked your slider but was unable to get it working properly as written in your app.js, so I adjusted some of the directional settings and slide-index logic to get it to work in our app. The problems I was having were similar to those mentioned in the comments of the onehungrymind post, so I thought maybe my solutions could be helpful. It's working very smoothly for us now. My version was pulling from our API to load the slides, so disregard that, of course. I also experimented with getting the slider to load three images at a time before abandoning, the remnants of which are still in this pull request, but commented out.