Update link to documentation

Point to the documentation on the website, where it's nicely rendered,
instead of the location in the Git repository.
Update Fedora image to Fedora 37
Add Steve Steiner to contributors list

Steve, sorry that your name got lost.
Remove mention of reStructuredText files

The documentation is no longer in the ftputil package. It's still
in the Git repository and of course on the website.
Fix ticket link

Now on Sourcehut :-)
Explicitly remove `__pycache__` under `.tox`

It seems that `find` by default doesn't recurse into "hidden"
directories and having `.tox/__pycache__` leads to problems in
`make dist`.
Remove `docs` target from `Makefile`

This is no longer supported.
Improve `README.release`
Remove Trac-specific todo items

We no longer have a version field or milestones.
Remove `make docs`

`make docs` is no longer necessary or supported. It was used to create
HTML pages from the reStructuredText files (which no longer exist).
Remove update item for `README.txt`

`README.txt` in the repository root directory has been changed to
`README.md`, and that file no longer contains version-specific

There's a file `doc/README.txt`, but that just mentions where to find
the documentation now, so this file doesn't contain version-specific
information either.
Run `make patch` to update version/date
Add new release 5.0.4 to `versions` page
Add announcement for version 5.0.4
Update version to 5.0.4
Explain cache invalidation in `FTPHost.rename`
Make cache invalidation in `rename` more robust

Always invalidate the stat cache entries for source and target, even if
an exception occurs. Check the recent commits with the changes to
`rmdir` and `remove` for the rationale.

ticket: 150
Invalidate cache for source and target

In `FTPHost.rename`, invalidate the stat cache for source and target.
This is obviously important for the source, but also for the target, in
case another file system item existed at the path before the rename.

Thanks to Maxim Martynov for the bug report and patch. :-)

ticket: 150
Test cache invalidation for `FTPHost.rename`

The missing cache invalidation was reported by Maxim Martynov, and he
provided the patch in the following commit. Thanks!

ticket: 150
Set up first file for deletion

This is important if the rename fails and the file stays at its old