Enhancements for twig extension

Enhancements for twig extension

- Fix extension memory leak
- Fix gcc compile warning (cast to const char *)
- Add TWIG_HAS_DYNAMIC_PROPERTY
- Remove the previous translation of 'array_key_exists($item, $object)'
  into TWIG_ARRAY_KEY_EXISTS when checking object property because what
  it really means is property_exists which has already been handled by
  TWIG_HAS_PROPERTY and TWIG_HAS_DYNAMIC_PROPERTY
- Fix native extension spacing