Fix UTF-8 representation of non-ASCII characters

[orviz]

Closes #251: add ensure_ascii=False to the json.dumps call to ensure raw UTF-8 representation of non-ASCII chars.

I have structured this PR in two commits to follow a TDD approach:

• The first commit adds a failing test case that asserts correct UTF-8 representation.
• The second commit provides the fix.

You can verify the assert errors by checking out the first commit and running the new test.

[simleo]

Thanks for this contribution! Before merging, I need you to update author and copyright info. Author info is in CITATION.cff, setup.py and rocrate/__init__.py. Copyright info is in README.md, rocrate/__init__.py and Python file headers. You can see 09bff64 and 04128fa for an example of similar changes.

[orviz]

@simleo I hope that the requested information has been properly added, such as prepend the author name in the author related files. Thanks!

[simleo]

@orviz sorry, I forgot to highlight the fact that authors are in alphabetical order by surname, in all files where they appear. Could you put them in the right order?

[orviz]

@simleo done!