Now the tail have a fixed size. It actually makes everything simpler. I took
order_min = -1 and order_max = 8. This makes the tails compatible with the
previous implementation. However we might want to change this to something like
-10, 10 so that they are self-contained. This commit should also fix issue #11.
- has_view_type_tag mechanism was replaced by a decltype long ago.
Cleaning since it seems to work on all supported compiler now.
- removed add_views : not used any more.