* 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)
* allow to replace std:: with custom implementations
* add examples (and credits) from @alanjfs :)
* static reflection, hint: template<> meta_type_t<Type>: meta_descriptor<name, func..., props..., etc...> (see #342)
* update documentation for meta, it contains less than half of the actual feature

WIP:
* make it easier to hook into the type system and describe how to do that to eg auto-generate meta types on first use
* add observer functions aside observer class
 - introduce the component iterators for non-contiguous collections of entities (multi component views, observers, user defined collections)
 - snapshot: support for range-based archives
 - update snapshot documentation to describe alternatives
 - custom pools.
 - the Perfect Model.
 - page size 0 -> page less mode
 - add ::reach and rev iterators to proxy objects for faster and unsafe iterations
 - add example: 64 bit ids with 32 bits reserved for users' purposes
 - composable views and "faster views", deprecate non-owning groups
 - offset instead of pages in the sparse set? top level mask for sparse sets?