Proposal: Add Repo.select_all to return {row count, results} similar to update_all and delete_all

[danie...@gmail.com]

Currently, when fetching data with Repo.all/2, users have no way to obtain the count of

returned rows without either:

1. Calling Enum.count/1 on the results.

2. Running a separate Repo.aggregate.

However, database adapters already return the row count, Repo.all and Repo.all_by simply discards it by calling elem(1) on the {count, rows} tuple.