Upgrade to SLF4J 2; migrate to OSSRH Staging API

In this release, I finally upgrade to SLF4J 2.x. This has been a long time coming, and I apologize for letting this project languish so long.

To publish the new release, I migrated to the new OSSRH Staging API. I also upgraded all of the other plugins. As a consequence, I needed to add a bunch of missing JavaDoc and attach the sources. The addition of comprehensive JavaDoc has clarified several details about how to configure and use this logger.

I switched away from the slf4j-parent POM, which eliminated the issue I had previously with slf4j-api. All of the unit tests run successfully. With the upgrade to SLF4J 2.x, the logger factory is now obtained from a service provider instead of a static logger binder.

Build for Java 8; upgrade dependencies and plugins

In this release, I finally dropped support for Java 7. By building this library for Java 8, I'm able to upgrade dependencies to newer versions that resolve identified vulnerabilities.

NOTE: I was unable to update to the latest slf4j-parent release because the associated slf4j-api test JAR appears to lack corresponding updates to the test code, which results in a reproducible unit test failure.

Upgrade/optimize dependencies and plugins

This release contains no functional changes, but is instead focused on project housekeeping.

Publish an official release

This release marks the fourth year of the publication of the first artifacts from this project. Better late than never, I suppose.

In this release (in which I'm including the previous tag):

• Upgrade to the latest release of JUnit 4 (4.13.1)
• Switch from old-school Java version specification to Maven Toolchain
• Declare plug-in versions in a pluginManagement section of the POM
• Replace the deprecated version badge in README with a newer one