HTTP client interface generation

[StephanePaulus]

Would it be possible to also add a flag to generate either server side API or client side API interface.

I think the class would just need different types of annotation:

On the interface: @HttpExchange and the methods @PostExchange instead of @PostMapping...

[hauner]

If it is just switching annotations it will work. I haven't used the HttpExchange feature so I can't say if it is really that simple.

Probably quite easy to implement a first version. We would only need a client annotation factory and an option to switch to client mode. Then, by trying to use it we would find out where adjustments are required.