Marcel van Pinxteren

Add "preload" feature

2

We have to translate [Query.preload](https://hexdocs.pm/ecto/Ecto.Query.html#preload/3) and [Repo.preload](https://hexdocs.pm/ecto/Ecto.Repo.html#c:preload/3) into something like [AQL subqueries](https://docs.arangodb.com/3.3/AQL/Examples/CombiningQueries.html) ``` from p in Post, join: c in assoc(p, :comments), preload: [comments: c] ``` should translate into ```...

Let's try to provide the same level of docs as Ecto and Postgrex. Undocumented features: - Create edge collections - Preload feature

After some experimenting, a few areas arose, where we need to make changes: - concurrent migrations was introduced The Adapter behaviour expects `lock_for_migrations` - Ecto.Date and Ecto.DateTime are now fully...