[FEATURE] Fluid Tag Builder: Allow empty attributes

When using the Fluid Tag Builder to create tags an attribute can only be
set as a key/value pair. It should be possible render attributes with
the "empty attributes syntax".

http://www.w3.org/TR/html-markup/syntax.html#syntax-attributes

Releases: master
Resolves: #67372
Change-Id: Iae76f2eb82af79ad36e6a1f1d2485fa2070090df
Reviewed-on: http://review.typo3.org/40139


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>