Allow marking certain tags (like <script>) as not being allowed to be self closed.
Per http://stackoverflow.com/questions/3558119/are-self-closing-tags-valid-in-html5, it is a bad idea to use '<p/>'-style syntax under pretty much any circumstance -- so we now never use it.

close_void_tags now differentiates between outputting "<hr>" and "<hr></hr>", still defaulted to true, since it requires less knowledge of exactly which tags are void or not if you do close a void tag.
Per http://www.colorglare.com/2014/02/03/to-close-or-not-to-close.html and the W3C HTML5 validator, closing a void tag like "<hr></hr>" is invalid -- so don't do that.