Revert 'logback' to version 1.3.15 to maintain compatibility with Java 8

I broke compatibility with Java 8 by upgrading logback to version 1.5.13. This release reverts logback to version 1.3.15 to restore Java 8 compatibility.

Migrate to OSSRH Staging API; update dependencies

This release was primarily devoted to migration from the retired Sonatype OSSRH system to the new OSSRH Staging API. I also upgraded to the latest release of Logback (version 1.5.13) and the latest releases of all Maven plugins.

The new JavaDoc plugin adds more documentation requirements, so all non-private classes, methods, and fields are now documented.

Upgrade dependencies to latest versions

In this release, I upgraded to the latest releases of TestNG and LogBack. This also required upgrading to JUnit Jupiter API, which is required by the LogBack tests JAR.

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.

Upgrade to the latest release of 'logback'

logback-testng-1.3.5

[maven-release-plugin] copy for tag logback-testng-1.3.5

Upgrade dependencies and plugins (part 2)

This release is a continuation of the project housekeeping contained in the previous release.

Upgrade dependencies and plugins

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

Upgrade to the latest release of JUnit 4

This release upgrades to the latest release of JUnit 4 (4.13.1)

Add handling for UnsupportedClassVersionError

Catch UnsupportedClassVersionError to avoid instantiation failure, which was causing test runs to fail during start-up.

Fix TestNG version conflict; don't depend on Guava

While working on a different project, I discovered that this appender could trigger version conflicts by loading older versions of TestNG classes. I resolved this issue by replacing direct references to these classes with equivalent code implemented via the Java reflection API.

I also removed the dependence on Google Guava. I was only using one class from this library, for an operation that was easily implemented with standard Java features.