results.json log is now merged at the feature level

Note This is to be considered a breaking change to the api, as the results file produced has changed its format slightly. It now aligns with how default Cucumber groups logs (Scenarios are grouped and nested with a feature, we currently dupe feature per scenario).

This also injects the value used from a scenario outline into the log data. Cucumberjs v2+ allows for custom formatters to address this, but I don't want to constrain versions so tightly.