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
* 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 and what about snapshot?
* allow for built-in parallel each if possible
* allow to replace std:: with custom implementations
* types defined at runtime that refer to the same compile-time type (but to different pools) are possible, the library is almost there
* add opaque input iterators to views and groups that return tuples <entity, T &...> (proxy), multi-pass guaranteed
* allow for custom stomp functions
* custom (decoupled) pools ==> N-buffering, shared components, multi-model, hibitsets, and so on
  - explore the possibility to wrap other backend with a XHandler component
* snapshot rework/deprecation
  - create(hint: entity) -> force-create
  - assign<T...>(first, last)
* use unordered_map for named pools and context variables:
  - use direct access (pool-like) also for context variables
  - allow for key/value variables where the key is an ENTT_ID_TYPE
  - improves multi-stomp
* add examples (and credits) from @alanjfs :)
* static reflection, hint: template<> meta_type_t<Type>: meta_descriptor<name, func..., props..., etc...>
* ENTT_NAMED_TYPE -> ENTT_EXPORT and add also ENTT_EXPORT_WITH_NAME
* meta: members+class as fake functions, is it possible?
* meta: export implicitly generated named types if possible
* add meta support to registry:
  - entity for each component
  - opaque get
  - and so on (I'm lazy) :)
* registry::each to iterate all components of an entity
* named types: almost-stable index optimization for direct access to pools, no more linear searches
  - can implicitly generate types for meta benefit from a similar approach?
* detect family on a macro based model
* is it possible to make named type constraints namespace-free?
* stomp -> merge (naming is hard as heck, it's known thing)
* observer: user defined filters (eg .replace<T, &function> or .group<T, U, &func>)
* any-of rule for views/groups (eg entity has A and any of B/C/D)
* sparse set: there exists an alternative to paginated sparse arrays?
* see warning (vs2017 only): d:\a\entt\entt\src\entt\entity\registry.hpp(108)
* registry
  - ::assure -> pool_type<T> &
  - ::group improve, reduce code

* Mission: get rid of named types
  - make it possible to use custom generators (eg for plugins)
    * dispatcher
    * emitter
    * registry
    * meta
    * monostate
    * locator
  - families should be defined as out-of-class to guarantee the same identifiers for the same types
  - update doc: family, dispatcher, emitter, registry, meta, across boundaries
  - update tests