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
* snapshot rework/deprecation
* add examples (and credits) from @alanjfs :)
* static reflection, hint: template<> meta_type_t<Type>: meta_descriptor<name, func..., props..., etc...>
* add meta support to registry (eg entity for each component and opaque get)
* allow for custom stamp functions
* observer: user defined filters (eg .replace<T, &function> or .group<T, U, &func>)
* use underlying_type as entity type within pools and registry? it would make different registries work together flawlessy
* can we write a bool conv func for entt::entity that silently compares it to null?
* stamp makes sense only when the list of components is empty
* remove registry::reset, add renage-destroy to sparse set and improve range-remove in the registry
* any-of rule for views/groups (eg entity has A and any of B/C/D)
  - get -> all, exclude -> none