dart: Parser is nog generated using Berp

[mpkorstanje]

🤔 What's the problem you've observed?

The Gherkin Parser for Dart is not generated using Berp. This is a problem because:

As of May 2016 Gherkin is implemented in 8 languages. This number is likely to increase to a dozen within a year or two. Very few programmers are intimate with all those languages. Therefore, in order to make it as easy as possible to refactor, fix bugs, add features and release packages it is essential that all implementations have a similar structure.

CONTRIBUTING.md - consistency between implementations

✨ Do you have a proposal for making it better?

Either:

• Use Berp to generate the parser.
• Remove Dart.

📚 Any additional context?

There are no acceptance tests for the Dart parser implementation #30