Use the same face for 'require' as for 'defmacro'

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Add a few macro-related builtins to th highlight list

quasiquote, unquote and unquote-splice should be highlighted as builtins
too.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>