Implement writer::JUnit (#50)

[ilslv]

Resolves #50

Synopsis

For now cucumber output can't be parsed by default CI tools.

Solution

Implement writer::JUnit

Checklist

• Created PR:
  • In draft mode
  • Name contains Draft: prefix
  • Name contains issue reference
  • Has assignee
• Documentation is updated (if required)
• Tests are updated (if required)
• Changes conform code style
• CHANGELOG entry is added (if required)
• FCM (final commit message) is posted
  • and approved
• Review is completed and changes are approved
• Before merge:
  • Milestone is set
  • PR's name and description are correct and up-to-date
  • Draft: prefix is removed
  • All temporary labels are removed

[ilslv]

Security audit will be failing until chronotope/chrono#578 is merged

[ilslv]

Note for future review: to better visualise .xml output I recommend using xunit-viewer

[tyranron]

@ilslv junit-report 0.7 is out, so we can finish this.

[ilslv]

FCM

Implement outputting JUnit XML report (#147, #50)

- impl `writer::JUnit` behind `output-junit` Cargo feature
- make `writer::Basic` generic over `io::Write` implementor

[tyranron]

@ilslv mentioning in Book and in README was missing 😕

[tyranron]

If the parent trait doesn't impose Sized requirement, then using T: ?Sized is very vital in such cases as allows blanket impl to propagate onto trait objects.