Promotion InterpreterExpressions to lambda expressions

[metoule]

When a method parameter is a fully closed generic type (ie doesn't depend on a method generic's parameters), we never converted the parsed lambda expression to an actual expression.

Example:

[Test]
public void Lambda_Issue_262()
{
    var list = new List<int> { 10, 30, 4 };

    var options = InterpreterOptions.Default | InterpreterOptions.LambdaExpressions;
    var interpreter = new Interpreter(options);
    interpreter.SetVariable("b", new Functions());
    interpreter.SetVariable("list", list);

    var results = interpreter.Eval<List<int>>(@"b.Add(list, t => t + 10)");
    Assert.AreEqual(new List<int> { 20, 40, 14 }, results);
}

public class Functions
{
    public List<int> Add(List<int> list, Func<int, int> transform)
    {
        return list.Select(i => transform(i)).ToList();
    }
}

In that case, Func<int, int> is a fully closed generic type, and thus t => t + 10 was never converted to the proper Linq expression.

Note: I also fixed a bug where in b.Add(list, t => t + 10), list, t was improperly seen as the two arguments to the lambda expression.

Fixes #262