Fixed bug that caused "scroll-to-top" animation to create endless loop.

https://github.com/cferdinandi/smooth-scroll/issues/24
Updated variables for more accurate easing math when scrolling to top of page.

https://github.com/cferdinandi/smooth-scroll/pull/25#issuecomment-325667
29
Fixed back button behavior when using `data-url` feature.

https://github.com/cferdinandi/smooth-scroll/pull/18
Merge branch 'back-button'
Update URL before animation, and fix back button behavior in Firefox.

https://github.com/cferdinandi/smooth-scroll/pull/27
https://github.com/cferdinandi/smooth-scroll/issues/26
Fix back button behavior in Chrome.

https://github.com/cferdinandi/smooth-scroll/issues/26#issuecomment-3317
2325
Set data-url to true
Updated IIFE
Remove extra whitespace
Switched to a data attribute for the toggle selector.

Also…
  * Added namespacing to IIFE.
  * Updated looping method and event listener.
Updated data-scroll-header data attribute
Reverted to `Array.protype.foreach` loops.
Merge branch 'master' of https://github.com/cferdinandi/smooth-scroll