Feature/issue 234 add scenario attach method

[kenhosr]

Description:

• Fix Embedding made screenshot into cucumber json report #234, add scenario.attach method

• Added scenario.attach method, so that you can add comments and/or screenshots to the cucumber-report.json file, and then you can convert the .json file to HTML report file

• Referred to this https://github.com/gkushang/cucumber-html-reporter/blob/4ed7e774f93c54ecd71a051d414a6d30305694ec/lib/reporter.js , which will convert step.embeddings to Show Info+

An example usage:

1. update your conftest.py by implementing the hook: pytest_bdd_after_scenario
   https://gist.github.com/kenhosr/3cb60efce5481d25967479e67f7edb76

2. run your test using: pytest --cucumber-json=cucumber_report.json

3. convert the .json to .html by following instructions here:
   https://github.com/gkushang/cucumber-html-reporter

Sample Report:

[codecov-io]

Codecov Report

Merging #329 into master will decrease coverage by 0.12%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #329      +/-   ##
==========================================
- Coverage   95.64%   95.51%   -0.13%     
==========================================
  Files          57       57              
  Lines        2202     2208       +6     
  Branches      184      184              
==========================================
+ Hits         2106     2109       +3     
- Misses         65       68       +3     
  Partials       31       31

Impacted Files	Coverage Δ
tests/feature/test_cucumber_json.py	96.96% <ø> (ø)	⬆️
pytest_bdd/reporting.py	92.42% <ø> (ø)	⬆️
pytest_bdd/cucumber_json.py	92.85% <ø> (ø)	⬆️
tests/feature/test_report.py	82.5% <ø> (ø)	⬆️
pytest_bdd/feature.py	98.14% <50%> (-1.1%)	⬇️

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[kenhosr]

found out an issue that when use Scenario Outline, it will attach data multiple times depending on the Examples table size. I will fix it later.

[robsonpolicarpo]

Hi! This branch will go to merged with master? Any prevision?

[david-vankampen]

@kenhosr is it possible to revisit this one and freshen it up for merging? It seems like a very useful feature.

Also, the gist linked here seems incorrect/unrelated:

update your conftest.py by implementing the hook: pytest_bdd_after_scenario
https://gist.github.com/kenhosr/3cb60efce5481d25967479e67f7edb76

could you freshen that up as well? Thank you!

And finally, an additional thought: pytest-nunit also has the add_nunit_attachment feature here... is it possible/beneficial to piggyback off of that if it exists, so as to reduce duplication?