Add smooth scrolling to in-page anchors.

smoothscrolling.js

$(document.body).on('click', '[data-smooth-scroll]', function(e){
  e.preventDefault();
  $('html,body').animate({scrollTop:$(this.hash).offset().top}, 500);
  if (Modernizr.history) window.history.pushState({}, this.hash, this.hash);
});