* Remove unused `report_progress_in_percent` option from step
* Remove `use_custom_progress_increment` option from the step because we can figure it out by looking at the progress
* Introduce `StepTracker` to for logging warnings and errors and tracking step progress
* Make it easier to log warnings and errors in all methods of `Step` without the need to pass around a `stats` object
* Updates GitHub Actions
* Switches from `bundler/inline` to an optional group in the `Gemfile` because the previous solution didn't work well with rspec
* Adds the converter framework and tests
* Allows loading private converters (see README)
* Switches from multiple CLI tools to a single CLI
* Makes DB connections reusable and adds a new abstraction for the `IntermediateDB`
* `IntermediateDB` acts as an interface for IPC calls when a converter steps runs in parallel (forks). Only the main process writes to the DB.
* Includes a simple example implementation of a converter for now.
