entt/TODO

* long term feature: templated generic vm
* long term feature: shared_ptr less locator
* long term feature: shared_ptr less 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
* runner proposal: https://en.wikipedia.org/wiki/Fork%E2%80%93join_model https://slide-rs.github.io/specs/03_dispatcher.html
* work stealing job system (see #100)
* meta: sort of meta view based on meta stuff to iterate entities, void * and meta info objects
* hashed string: add implicit check on construction for uniqueness (optional)
* allow for built-in parallel each if possible
* tags revenge: if it's possible, reintroduce them but without a link to entities (see #169 for more details)
* empty components model allows for shared components and prefabs unity-like
* allow to replace std:: with custom implementations
* cleanup - see https://github.com/skypjack/entt/commit/ad5cedc08c83e8cbcc8aaeac9634d44624ffe35a#commitcomment-32380903
* allow to sort groups (::respect can already work with begin/end instead of a whole sparse set)
  -it would ease by far the group trick for hierarchies that requires otherwise more boilerplate
* allow some features by component type (eg registry.assign(entity, component);
  - it could be possible for eg default constructible types by storing aside (pool data) erased functions
  - does it worth it?
* events on replace, so that one can track updated components? indagate impact
  - 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)
  - from Tommaso on discord view<Health, Transform>().where<Health>([](h) {h > 5}).where<Transform>([](t) {t.inside(aabb)});