Added TODO item in D4ScriptEngine.
Added binding subroutines and variables via the javax.script ScriptContext and Bindings API.
Added D4Var.SCope.set() method.
Fixed to update D4Var's to the scripting engine.
Added D4ScriptEngine.registerVariable() to facilitate the update.
Updated unit test to reflect changes.
Added initial D4ScriptEngineFactory.
Added associated unit test.