Follow CR-html5-20140429.

Now interactive elements are omitted from HTML5 and postponed to HTML
5.1. Stay tuned.

See also: http://www.w3.org/TR/2014/CR-html5-20140429/

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Add view-mode.vim and test.

Reference: http://www.w3.org/TR/2012/REC-view-mode-20120619/

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>