Improved the renderViews method by allowing it to render only some of the children views.

We found that renderViews was a little too brute force for some of our scenarios (https://digitalpigeon.com) as it would render all the children views when we only needed to render some of them. This change essentially changes the renderViews method with the same arguments as getView, plus an extra array option...

Example usage:
```
var views = [];
_.each(addFiles, (function(_this) {
  return function(file) {
    var subView;
    subView = new FileView({
      model: file
    });
    views.push(subView);
  };
})(this));
this.insertViews({
  ".files": views
});
this.renderViews(views).then((function(_this) {
  return function() {
    _this.reorderFiles();
    _this.scrollToEl(views[views.length - 1].$el);
  };
})(this));
```

p.s. I've written tests but couldn't get grunt working, it's late and I want some dinner and a beer. If it's something you guys are interested in I'll figure out how to get grunt going.