Ecto version 3.X.X support - alpha release

This release is our first take at providing support for Ecto version 3.X.X!

Currently, all of the existing tests are passing and we've been able to successfully integrate this into one of our applications seemingly without problem - but this release probably should not yet be treated as production-ready.

If you are already using this adapter in conjunction with Ecto version 2.X.X, you'd want to follow Ecto's upgrade guide in terms of identifying any breaking changes (most notably, the adapter is no longer specified in your app's configuration, but rather in the module where you define your app's repo). I've added a bit about this in the README.

There are a few notable things-to-do, for which I'll be creating "To-do" issues:

• Consider adding support for stream/5 (see `lib/ecto_adapters_dynamodb.ex)

• Consider adding support for checkout/3 (see `lib/ecto_adapters_dynamodb.ex)

• Consider adding support for lock_for_migrations/4 (see `lib/ecto_adapters_dynamodb.ex)

• Clean up/improve tests and add additional test cases

  • make sure tests cover all types specified in decode_type/2, including MapSet and embedded MapSet
  • add tests for scenarios where insert_nil_fields config option has been set to false
  • add tests for scenarios where remove_nil_fields_on_update config option has been set to true

• Generally improve documentation

Don't hesitate to jump in and get your hands dirty! We appreciate all support from the community.