Restructure gherkinrc file to place rules in rules

[andrewnicols]

This change will allow for future changes to the gherkinlint
configuration file for configuration of non-rule based features.

This relates to your suggestion to add an additionalRules configuration directive.

Let me know what you think. I haven’t added any backwards-compatibility.

[vsiakka]

The changes look very good and thank for taking the time to do them.
I added a couple of very minor comments. Can you also update this file used by the demo command? https://github.com/vsiakka/gherkin-lint/blob/master/test-data-wip/.gherkin-lintrc

I think we should break compatibility and I can prep that with a major version bump. This will ensure that people don't install by accident the new version and it will prevent us from having to support multiple code paths which depend on the existence of a specific string in the keys of a user defined json file.

This also gives flexibility to add more configuration to the file in the future and it's in par with what .eslinrc does

[coveralls]

Pull Request Test Coverage Report for Build 605

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 96.948%

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Totals
Change from base Build 604:	0.01%
Covered Lines:	746
Relevant Lines:	759

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 6413256063

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.3%) to 96.777%

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Files with Coverage Reduction	New Missed Lines	%
dist/config-verifier.js	1	96.0%
dist/config-parser.js	2	89.74%

Totals
Change from base Build 6413242402:	-0.3%
Covered Lines:	784
Relevant Lines:	799

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💛 - Coveralls