Hat's off to JDotSoft

Integrated JarClassLoader from JDotSoft. Only took me about an half hour to figure the whole thing out. For my tastes, much simpler and more embeddable than One-JAR.

Now the dist ant target builds a standalone, executable jar-- diffkit-app.jar. For embedded applications, users simply explode the diffkitapp.jar, the diffkit library jar is in the root, and all dependent jars in lib/.