Add README; add JUnit to library; remove Disruptor; update JAR specifica...

...tions
I was looking into the options the other day. As you suggested, it seems like Gradle is probably the way to go. It sounds like it's safe to ask a developer to have/get a build tool like Gradle, but not an IDE like IntelliJ, is that right?

And thanks! I tried to make it useful, even if I wasn't sure whether depending on an IDE was fair game.