Fix Expression generation in compilation

[unarist]

I've fixed two issues on Expression generation in compilation

• Variable access to reference types causes ArugmentException

  class Test {
    public object TestObject = new object();
  }
  var template = "Result is {{TestObject}}";

  throws ArgumentException: Argument types do not match.

• Model class which has ToString() method causes ArugmentException

  class Test {
    public string TestString = "Hello";
    public override string ToString() { return base.ToString(); }
  }
  var template = "Result is {{TestString}}";

  throws ArgumentException: Method 'System.String ToString()' declared on type 'Test' cannot be called with instance of type 'System.String'.

Also, I have added test cases for these situations.

[Romanx]

Hey,

This was released in Nustache v1.16.0.1. Thank you for your contribution!