gherlint

New checks:

• unused-parameter
• empty-background
• outline-could-be-a-scenario
• consider-using-background
• examples-outside-scenario-outline
• duplicated-tag

Other changes:

• unparseable-file is now issued for all nodes that offend the gherkin parser together with more error information provided by it
• missing-parameter now clearly states what parameter is not defined in the examples
• If gherlint patches the file contents with a forgotten # language tag the line numbers for messages
  are no longer shifted
• Types of And and But steps are now inferred correctly
• New command fix-language-tags to automatically add or fix missing or incorrect language tags
• Rename some message codes to have a defined structure: each checker has its own hundreds digit.

New checks:

• missing-language-tag
• wrong-language-tag
• unparseable-file

Other changes:

• gherlint can now automatically detect the language used and make sure that it can parse the files
  even without a # language token present.

New checks:

• missing-given-step
• missing-when-step
• missing-then-step
• empty-scenario
• empty-feature
• file-has-no-feature
• missing-parameter

Other changes:

• Support for Background
• Determination of step type independent of language
• Distinction between Scenario and Scenario Outline independent of language

First release on PyPI.