Add mix tasks conveniences and a migration generator
Binary values should be wrapped in Ecto.Binary[]
Improve migrations info in README
Add a Repo generator and include app_dir by default
Improve generator workflow with ECTO_EDITOR
Break apart PG integration tests and add test/support directory
Move repository implementation to Ecto.Repo.Backend

The main reason is to clean up the Ecto.Repo implementation
which was getting too long and confusing. We also refactored
`start_link` to pass the already parsed URL to the adapter.
Update README.md
Update README.md
Support multiple commands in migration

Postgrex only allows a single command per query, return a list of
commands from the migration to run multiple commands per migration.
Improve association docs

Explain difference between has_one and belongs_to
Closes #88.
Add `group_by: var` syntax

Will group on all fields on var's entity.
Closes #89.
Move Ecto.Model.Queryable to its own file, improve docs and auto-import from/1 and from/2
Add Ecto.Validator
Add some validator predicates
Add `group_by: var` example
Add Ecto.Model.Validations
Store @ecto_source and @ecto_entity in Ecto.Model
Support string type as field default
Run validator on dicts as well