* custom allocators and EnTT allocator-aware in general (long term feature, I don't actually need it at the moment) - see #22
* scene management (I prefer the concept of spaces, that is a kind of scene anyway)
* debugging tools (#60): the issue online already contains interesting tips on this, look at it
* define basic reactive systems (track entities to which component is attached, track entities from which component is removed, and so on)
* define systems as composable mixins (initializazion, reactive, update, whatever) with flexible auto-detected arguments (registry, views, etc)
* registry::create with a "hint" on the entity identifier to use, it should ease combining multiple registries
* deep copy of a registry (or use the snapshot stuff to copy components and keep intact ids at least)
* is it possible to iterate all the components assigned to an entity through a common base class?
* optimize for empty components, it would be a mid improvement in terms of memory usage
* can we do more for shared libraries? who knows... see #144
* work stealing job system (see #100)
* make view copyable/moveable
* reflection system (maybe)
* C++17. That's all.
* AOB
* lower case names (?)
* tag_t and the others, create constexpr var