Advance notice of intention to stop releasing PHAR file release artifacts

[jrfnl]

Split off from #157

At this time, releases of the project can be obtained in the following ways:

• Packagist (Composer package)
• Download of the release zip from the Releases page or via a GH permalink.
• Download of a PHAR file for the release from the Releases page or via a GH permalink.
• Clone the repo and check out the desired tag.

The first option (Packagist) is, by far, the most popular.

And based on these download stats for the PHAR files, the number of users downloading the PHAR file(s) is negligible.

So the proposal is to drop support for releasing as a PHAR file at some point in the foreseeable future.

Consider this a heads-up. If anyone has objections or a specific usecase which could justify continued PHAR file releases, please make yourselves known and make your case.