Carry attrs, classes from one element to another.
Install with component(1):
$ component install yields/carry
function Widget(el){
this.el = carry(el, tpl.cloneNode());
}
new Widget;
new Widget(el);if a is null a clone of b will be returned.
otherwise b's attrs and classes are merged with a,
returning a.
Carry over attributes from b to a.
Carry over classes from b to a.
MIT