Preserving passed attributes

Currently the helper passes a string to $html->tag(), which that function assumes to be a string of class names. I rewrote things a bit to preserve all passed attributes. The existing array merge wasn't working quite right, either, as the passed attributes are an array and $activeClass is a string.

Don't mind the commit message. it doesn't HAVE to be an array. The tag function just makes assumptions when it's not.