Simplify expression stack parsing
Simplify expression stack parsing

justjohn/twig.js,dave-irvine/twig.js,dave-irvine/twig.js,dave-irvine/twig.js,twigjs/twig.js,justjohn/twig.js,twigjs/twig.js,justjohn/twig.js,twigjs/twig.js