Fix interpolated data tables and doc string arguments

[mpkorstanje]

⚡️ What's your motivation?

The json report should use the pickle table and doc strings rather than
those from the step. The former are interpolated with values from
examples, the latter are not.

Fixes: #28

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.