Prefer pathlib for read/write operations

[jaraco]

• Rely on pathlib when reading and writing simple text.
• Universal newlines is the default, so remove the comment.

Description

While working on #577, I noticed it might be nice to leverage pathlib for reading and writing files. This approach avoids adding nesting and with blocks by utilizing read_text and write_text.

This PR depends on #577 and should be rebased after merging that one.

Checklist

• [x] Make sure changes are covered by existing or new tests.
• [x] For at least one Python version, make sure local test run is green.
• [x] Create a file in src/towncrier/newsfragments/. Describe your change and include important information. Your change will be included in the public release notes.
• [x] Make sure all GitHub Actions checks are green (they are automatically checking all of the above).
• [x] Ensure docs/tutorial.rst is still up-to-date.
• [x] If you add new CLI arguments (or change the meaning of existing ones), make sure docs/cli.rst reflects those changes.
• [x] If you add new configuration options (or change the meaning of existing ones), make sure docs/configuration.rst reflects those changes.

[jaraco]

Oh, this change fails on Python 3.9 and earlier due to the newline parameter only being added in that edition.

If this proposed transition is acceptable, I'd be tempted to wrap the offending call in a compatibility wrapper (something that would signal its removal after Python 3.9 support is dropped), but I'm not sure it's worth the effort.

[jaraco]

The coverage failure doesn't make any sense:

Name                       Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------------------
src/towncrier/_writer.py      25      0     10      1    97%   20->exit
----------------------------------------------------------------------
TOTAL                        677      0    321      1    99%

Does 20->exit mean that the coverage check wants to see an exception occur in the context in order to check both __exit__(None, None, None) and __exit__(type, val, ctx)? That's absurd and didn't need to be checked before. Or is it a bug in coverage, where it's failing to detect that the context is exited at all (which it must for the function to return)?

[adiroiban]

Thanks. If you are happy with this PR, feel free to merge.

[jaraco]

Thanks. If you are happy with this PR, feel free to merge.

I would merge, but something's wrong with credentials. I'm a member of towncrier-contributors, yet I have no option to merge. I've signed out and back in but yet can't merge. It says I need write access to merge.

[adiroiban]

Sorry. My bad. I set the wrong permissiosn for the team. I have merged it, but in the future you should be able to merge. Thanks again!