Add the module path to the definition name to avoid name collisions

[TobiasDeBruijn]

This PR intends to fix #357, but uses an alternative approach to #358.

With this PR, the behaviour will be as follows:

mod foo {
    pub mod bar {
        use paperclip::actix::{web, api_v2_operation, Apiv2Schema};
        use serde::Serialize;

        #[derive(Serialize, Apiv2Schema)]
        pub struct Response {
            bar: i32
        }

        #[api_v2_operation]
        pub fn b() -> web::Json<Response> {
            web::Json(Response { bar: 10 })
        }
    }
}

results in the following spec:

  foo_bar_Response:
    type: object
    properties:
      bar:
        type: integer
        format: int32
    required:
      - bar
...
          schema:
            $ref: '#/definitions/foo_bar_Response' 

The advantage of this PR over #358 is that the generated spec is always the same for the same input code.

The name is determined by taking the output of std::module_path!(), removing the first 'component' (i.e. the crate name), then joining with _ as a separator.

This will not break code backwards compatibility, but it will break spec backwards compatibility, i.e. the generated spec is different from how it would be without this PR

[tiagolobocastro]

Hey @TobiasDeBruijn, as discussed previously this should be opt-in only - we can probably do that by hiding this behind a feature gate?

[tiagolobocastro]

Looks good, can we add a test for this feature?

[TobiasDeBruijn]

I'll give writing a test a shot!

[tiagolobocastro]

Thanks @TobiasDeBruijn !