Add example for Custom Types

[FranchescaMullin]

Can you provide a complete example of how to set up an endpoint that uses custom types?

I was trying the sample code in the documentation, but it was not clear to me where in the project the code to set up the object mapper should go, or how I can have a custom type struct that contains std::string members .

Would really love to get this part working, as it otherwise seems like a promising framework.