Add option to include contextual information in code fragments

[just95]

When a scenario is imported to Testomatio, the corresponding source code from the *.feature file is also uploaded. However, seeing just the scenarios code might not be sufficient or even misleading. Most importantly, there is currently no way to see the steps of a Background section on Testomatio.

This PR adds CLI flags to include the source code of relevant Background sections as well as the names, descriptions and tags of parent features and rules.

$> npx check-cucumber --help
  ...
  --include-features           Add description of feature to scenario code
  --include-rules              Add description of parent rule sections to scenario code
  --include-backgrounds        Add description and steps of relevant background sections to scenario code

For example, when all three CLI flags are set, the tool will now extract the following code fragment for "Scenario 2.2" from example/features/rules.feature:

Feature: A feature with multiple rules
  Description of the feature

  Background:
    Given all rules have something

  Rule: Rule 2
    Description of second rule

    Background:
      Given the second rule has something

    Scenario: Scenario 2.2
      Description of second scenario

      Given I have something
      When I do something
      Then something happens

This PR depends on the support for rules added in #38. The getLocations function added in #38 is also reused to extract the correct source code fragments for features, rules and backgrounds. The main change is the implementation of a new handler for the Background keyword in getSourceCode and the addition of a context variable to keep track of the source code of rules and backgrounds.