* added basic_sparse_set<E>::current to return known version of identifiers in set
* sparse arrays also contain updated entity versions, no more unused bits
* basic_sparse_set<E>::contains performs a strict version check
* sparse sets manage correctly foreign entities in all cases now
* no tombstone checks for multi-type views, zero-cost pointer stability model
* removed meta_type::is_integral (no alternative provided)
* removed meta_type::is_floating_point (no alternative provided)
* added meta_type::is_arithmetic, prepare for auto-generated implicit conversions
* removed meta_type::rank (no alternative provided)
* removed meta_type::extent (no alternative provided)
* removed meta_type::rmove_extent (no alternative provided)
* removed meta_type::remove_pointer ((*any).type())
* add owned_t utility
* change view def to basic_view<T, get_t<C...>, exclude_t<E...>>
* change group def to basic_group<T, owned_t<O...>, get_t<G...>, exclude_t<E...>>
* remove view dispatcher (reduce instantiations)
* make basic_view::traverse use the local policy
* review of entt_traits design
* added static constexpr member function entt_traits::to_integral
* added static constexpr member function entt_traits::to_entity
* added static constexpr member function entt_traits::to_version
* added static constexpr member function entt_traits::to_type
* custom class identifiers must expose member type entity_field
* it's no longer required to specialize entt_traits (breaking change)
* const registry::view is no longer thread safe
* views are always valid when created from a registry, either const or not
* added a note to the doc about const registry and multithreading