Set the encoding option of the open() functions in the codes

[Surpris]

Brief

This pull request is relevant to Issue #207:

What' changed

Set encoding='utf-8' options to the following functions/methods and take some refactoring:

• read_metadata() in rocrate/metadata.py
• write() in rocrate/mode/file.py
• write() in rocrate/mode/metadata.py
• write() in rocrate/mode/preview.py

Note

There are no unit-test functions for the Metadata class, etc. It might be desirable to add some.

[simleo]

@Surpris since you're a new contributor I need you to update the authors section in CITATION.cff. I also need your copyright line to update the headers.

[Surpris]

@simleo,
Thank you for your request.
I tried to update CITATION.cff and the scripts that I had modified.
Please confirm whether the changes are what you expected.