Support alternate "@Annotation" style comment directives

[simonnix]

Is your feature request related to a problem? Please describe.
It is comprehensible that the Java style "@annotation" is somewhat what some other projects developpers of may want to use to annotate struct and functions and develop some tools.

I analysed the code (but did not test it) and did not find a way to make swag works well with other tools like golangAnnotations.

// @RestOperation( method = "GET", path = "/person/{uid}" )
func (s *Service) getPerson(c context.Context, uid string) (*Person, error) {
    ...
}

Describe the solution you'd like
It would be right to have an option on the command line to use a "namespace" annotations like "@Swag." :

// ShowAccount godoc
// @Swag.Summary      Show an account
// @Swag.Description  get string by ID
func (c *Controller) ShowAccount(ctx *gin.Context) {
}

**Describe alternatives you've considered**
Add an option to use another symbol for "@" (maybe "%").