Add staggering animations

[zewa666]

Add a nice way to define staggering animations. The current approach is that the user would have to define a custom animation-delay by himself:

.myrepeater.au-enter:nth-child(1) {
    -webkit-animation-delay: 1s;
}
.myrepeater.au-enter:nth-child(2) {
    -webkit-animation-delay: 2s;
}

maybe we could add a new class with a delay suffix which gets parsed by the animator. Something like this:

.myrepeater.au-enter.au-stagger-100 {
  ...
}

[zewa666]

Done with d57d22b