Commonpy

Changes in this release:
* New exception `ArgumentError`.
* `net(...)` makes slightly finer distinctions between `ServiceFailure` and `NetworkFailure` when it comes to addresses it can't connect to, and also raises `ArgumentError` in some cases such as passing a `data` keyword argument to a network `get`.
* `on_localhost(...)` logs slightly better debug messages.
* There are more test cases.
* `CITATION.cff` has been corrected and no longer describes the wrong repository.

This version merely changes a version dependency in `requirements.txt`. No other changes.

Changes in this release:

* At some point between versions 0.18 and 0.21.1 (current version), the `httpx` package changed the keyword argument named `allow_redirects` to `follow_redirects`, and our `network_utils` module functions broke as a result. This release updates `network_utils` to account for the change.
* The `requirements.txt` file now pins most dependencies to a specific version, to avoid situations where getting a newer version of a package might break existing code.
* The copyright year has been updated in various files.

This version introduces the `data_structures` module, and a new class, `CaseFoldDict`.

Changes in this release:

* Fixed a missing f-string in an exception message, plus guarded a few more exception message strings with `antiformat`.
* Added `CITATION.cff` file.
* Updated the `Makefile`.

Improve `flattened` to handle lists of dict keys.