TODO

* long term feature: shared_ptr less locator and resource cache
* custom allocators and EnTT allocator-aware in general (long term feature, I don't actually need it at the moment) - see #22
* debugging tools (#60): the issue online already contains interesting tips on this, look at it
* work stealing job system (see #100) + mt scheduler based on const awareness for types
* meta: sort of meta view based on meta stuff to iterate entities, void * and meta info objects (remove runtime views, welcome reflection)
* add opaque input iterators to views and groups that return tuples <entity, T &...> (proxy), multi-pass guaranteed
* allow to replace std:: with custom implementations
* custom (decoupled) pools ==> N-buffering, shared components, multi-model, hibitsets, and so on
* add examples (and credits) from @alanjfs :)
* static reflection, hint: template<> meta_type_t<Type>: meta_descriptor<name, func..., props..., etc...> (see #342)
* can we write a bool conv func for entt::entity that silently compares it to null?
* is it possible to make 0 the entity null?
* update documentation for meta, it contains less than half of the actual feature

Next:
* make it easier to hook into the type system and describe how to do that to eg auto-generate meta types on first use
* review multi component views to reduce instantiations once empty types are gone...
* add observer functions aside observer class

* WIP:
 - introduce the component iterators for non-contiguous collections of entities (multi component views, observers, user defined collections)

* WIP: snapshot rework
 - snapshot: support for range-based archives
 - update documentation to describe alternatives