Add struct annotation to avoid certain structs being processed as Models

[juampiq6]

For a larger scale API, that only wants to expose certain models to swagger, it's neccessary to be able to exclude certain structs so that they dont get parsed nor showed in the final Swagger doc.

I propose a simple annotation in a struct, comment just like @Description, this would be @Ignore or @Exclude

// This annotation would enable to omit this struct from being parsed
// @Exclude/@Ignore
type Foo struct {
	Bar        string 
	Blob      int
}