* fix and enhance support for custom ecto types (see example `Dlex.Geo` in tests)
* fix a types diff not handled proparly in `Dlex.Repo` in alter_schema
* enahnce decoding/encoding in `Dlex.Repo` to return errors
* enhance `Repo.all` to accept query parameters.
  To enable `Repo.all` automatically detect types and converts to types, please include at least `dgraph.type`.
  Recommended query returns to get keys:

    ```
    uid
    dgraph.type
    expand(_all_)
    ```