The application's configuration is stored using `ApplicationProperties`
which doesn't consider the *XDG Base Directory Specification*. There is
`File::userApplicationDataDirectory` but it also doesn't respect it
according to an upstream [bug report].

Supporting the full specification is more effort but just supporting
`XDG_CONFIG_HOME` already addresses the common issue of the home
directory being spammed with configuration files. So just read that
environment variable or use its default to set the `folderName`, with an
appended application name since the specification suggests to also use
a subfolder.

This is a breaking change for Linux users but since none are known at
the time it seems acceptable to just switch instead of supporting some
form of migration. It's also mentioned in the change log.

[bug report]: juce-framework/JUCE#1184

At least when updating JUCE this can be helpful to know the expected
version is used. It also buts a bit more information in the dialog,
making it look more informative.

This update allows building with ASIO support using the ASIO sources
bundled with JUCE. The documentation regarding a special build for ASIO
support is no longer needed.

The dual-licensing will remain for two reasons:

1. Any licensing change is always annoying.
2. The flexibility was valuable in the past, so it might also be worth
   it again in the future.

The script was removed in 2e263e2 so it
can no longer be used.

Use the [Changelog release] action to extract the relevant changes for
the version from the `Changelog.md` file.

[Changelog release]: https://github.com/marketplace/actions/changelog-release

The static values can just be made floats by using the `f` suffix.

The value returned by `getDoubleAttribute` is just cast to float, like
the next line already does it.

All callers of `updateGain` already have an `int`, except for
`setChannelVolume` where the single caller also has an `int`.

The only caller of `getInternalOutputChannelName` has `size_t` and the
function itself works with any numeric type.

The `entryIndex` is always an `int` in the caller and the called
functions.

Changed these function signatures to prevent warnings about integer
conversions with possible loss of data.

Call `getChildElement` only once, keeping the pointer for the following
calls. This was done to reduce the number of warnings that `size_t` is
converted to `int` with possible loss of data.

This reverts one change from c4f1cec
which had the side effect of `while (activeChannelIndex-- >= 0)` always
being true, resulting in an endless loop.

The first link is for downloading the latest release directly. The old
link wasn't working anymore anyways.

The second link is just the naming. Removed the version number as it's
not really that important.

The *Read the changelog* action failed with this error message:

    Error: Container action is only supported on Linux

Add a second job to run on Linux. This will read the changelog and do
the release, using the artifacts of the previous build job.

The name of the action was wrong, leading to:

    Error: Unable to resolve action actions/download-artifacts, repository not found

The publish job also started before the build job. Fixed by adding the
missing dependency.

When running the action GitHub showed a warning:

    Unexpected input(s) 'INPUT_CHANGELOG_FILE', valid inputs are ['entryPoint', 'args', 'tag_name', 'changelog_file', 'add_emojis', 'emoji_end_of_line', 'add_raw_changelog_link', 'allow_failure']

Remove the wrong 'INPUT_' prefix and use lower case as in the warning
and because it's nicer to read.

The changelog isn't an artifact but in the repository itself. So in
addition to downloading the build artifacts the repository must also be
checked out.