Empty action attribute is not rendered in HTML5

"The action and formaction content attributes, if specified, must have a value that is a valid non-empty URL"
(http://www.w3.org/html/wg/drafts/html/master/forms.html#attr-fs-action)
Merge pull request #209 from mhujer/html5-form-action-fix

Empty action form attribute should not be rendered in HTML5
Merge branch 'hotfix/209'

Close #209