Better handling of integration tests

This patch release provides more elegant handling of the integration test module, which will only be run when a local version of DynamoDB is running and properly configured - otherwise, they'll be gracefully ignored.

Fix README documentation

This patch release fixes some typos/layout issues in the README documentation.

Add transaction support

This minor version release adds support for DynamoDB transactions via two new public methods, transact_get_items/2 and transact_write_items/2.

See https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transaction-apis.html for an overview of DynamoDB's transactions.

Instructions for local testing

This app includes a set of integration tests that will run against local DynamoDB - this release includes instructions on how to set up the app to run those tests, as well as a slight reorganization of the config files and a method to make sure test tables are deleted after tests are run. See README for an overview of how to prepare for and run these tests.

Properly handle binary data

The DynamoDB docs indicate that binary data should be base64-encoded to be written as a Dynamo binary data type; this patch release fixes an issue where binary data was not being properly encoded/decoded.

Optionally decode DynamoDB sets to Elixir MapSets

When encoding Elixir MapSet data, the default behavior of this application is to convert that data to one of DynamoDB's three set types - number, string, or binary; however, DynamoDB sets will be decoded to Elixir List data.

This minor release adds a configuration option that allows a user to specify how to decode DynamoDB set types - the default will remain List, but setting decode_sets: true in the app's configuration will decode those set types to an Elixir MapSet.

This release also includes several other small bits of code cleanup and housekeeping, and adds additional test coverage.

Support billing mode

This release adds support for setting the billing mode for a table during calls to create_table and update_table.

For more info on billing modes: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BillingModeSummary.html