v2.10.0

What's new:

• Improved JsonataExtensions.ToSystemTextJsonNode — now it is able to create a JsonNode for an undefined token instead of throwing exeption. See discussion here. The node itself is not very useful, but at least it could be checked for it's kind like this.
• Exposed Eval.BuiltinFunctions class to provide for re-using standard functions when implementing custom ones. See #39
• Exposed Eval.FunctionToken and Eval.EvalProcessor.InvokeFunction() to provide for custom functions accepting other functions as arguments.
• Improved JsonataExerciser app: added ability to process output json with Json.Net or System.Text.Json conversion (actually results should be the same, but it seems to be handy):