[feature/twig] Docs/typehinting for Twig extension

PHPBB3-11598
[feature/twig] Nicer code for get_user_style.php()

PHPBB3-11598
[feature/twig] Spacing

PHPBB3-11598
[feature/twig] Clarify comment

PHPBB3-11598
[feature/twig] Add template test for ===, !==

PHPBB3-11598