Ability to call a method extension

[davideicardi]

It should be possible to write:

        var x = new int[] { 10, 30, 4 };

        var target = new Interpreter()
                                .Reference(typeof(System.Linq.Enumerable))
                                .SetVariable("x", x);

        Assert.AreEqual(x.Count(), target.Eval("x.Count()"));