Added support of the HTML5 form attribute
Merge pull request #51 from stof/html5_form

Added support of the HTML5 form attribute
Changed the base class for tests to avoid using the deprecated class
Fixed the deletion of cookie on Windows in some cases

When the current url is returned as /foo.php, dirname will return \ on
windows instead of / and the removal of the cookie will then fail.
Fixed the composer requirement to allow 1.6