Updated HTML5 void tags.

Void tags taken from http://www.w3.org/TR/html-markup/syntax.html#syntax-elements.
Removed isindex tag as it was deprecated since HTML 4.01 (source: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/isindex).
Merge pull request #4 from Munawwar/void-tags

Updated HTML5 void tags.