Add APIs for tasks to easily create/use a JRuby ScriptingContainer

[rtyler]

Relates to #20, #15 and future enhancements

We basically need some simple tooling to allow for building on top of an embedded JRuby scripting environment.

[ysb33r]

Thinking around loading jruby-complete.jar ...

In order to have this JAR available within the main Gradle runner, we have two options I believe

[1] Specify require version in buildscript

buildscript {
  dependencies {
    classpath 'org.jruby.jruby-complete:1.7.15'
  }
}

Relatively simple, but causes a conflict in UX. There is already a jruby.jrubyVersion and a `jruby.execVersion' that respectively controls the version for artifact building and executing ruby scripts. Now we are adding a 3rd way? Maybe not such a good idea

[2] Use a classloader. This is more complex to code, but is could actually utilise the jruby.jrubyVersion value and late-load the jar. However, we need to be sure that we only ever load one version of jruby-complete within the Gradle process. We also need to be sure as to when we are going to need this within the process. What if we start using ruby scripting as part of configuration? Since jruby.jrubyVersion is not fully set until project.evaluate() is called, we could end up in the nasty situation where we need to load a version of jruby only to be told later that it is the wrong version. Now option 1 suddenly looks better...

[rtyler]

We have JRubyExec now and I've not seen other needs for embedding Ruby in Gradle files so I'm going to close this