Use Gherkin parser as soon as it becomes available

[ehuelsmann]

The cucumber project started "Gherkin3", a project which allows to consistently parse Gherkin .feature files across languages (https://github.com/cucumber/gherkin).

[pjlsergeant]

Work in progress here: https://github.com/pjlsergeant/gherkin/tree/master/perl

[pjlsergeant]

This will break use of "Scenario" to mean "Scenario Outline", so I'm unsure about this.

[ehuelsmann]

The Gherkin release notes suggest that in Gherkin 6 Scenario Outline vs Scenario has been resolved:
https://github.com/cucumber/cucumber/blob/master/gherkin/CHANGELOG.md#6013---2018-09-25

[ehuelsmann]

After cucumber/common#694 gets merged the Gherkin parser has everything we need to drive cucumber tests: the generated pickles list all the scenarios and their steps that will be executed. This will also eliminate the need to parse Gherkin "ourselves".

[ehuelsmann]

I'm only inclined to go this way if we can have the protobuf library required to produce the wire protocol data be an optional component in the ecosystem.

[ehuelsmann]

An alternative would be to test our parser with the central testing corpus.

[ehuelsmann]

There's a fully updated Gherkin parser available now on CPAN!