* 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
* add examples (and credits) from @alanjfs :)

WIP:
* uses-allocator construction: dense map, compressed pair, any (with allocator support), cache, dispatcher, poly, storage/map/allocate_unique (with uninitialized_construct_using_allocator/construct_at), ...
* add an ENTT_NOEXCEPT with args and use it to make ie compressed_pair conditionally noexcept
* storage traits: mixin only, make views stop using traits, they can refer to storage<T> only
* process scheduler: reviews, use free lists internally
* runtime events (emitter)
* iterator based try_emplace vs try_insert for perf reasons
* registry: remove reference to basic_sparse_set<E>
* dedicated entity storage, in-place O(1) release/destroy for non-orphaned entities, out-of-sync model
* entity-only and exclude-only views
* custom allocators all over

WIP:
* add user data to type_info
* write documentation for custom storages and views!!
* make runtime views use opaque storage and therefore return also elements.
* entity-aware observer, add observer functions aside observer class
* deprecate non-owning groups in favor of owning views and view packs, introduce lazy owning views