code: func (c *Cors) HandlerFunc(w http.ResponseWriter, r *http.Request) {
  	if r.Method == http.MethodOptions && r.Header.Get("Access-Control-Request-Method") != "" {
  		c.logf("HandlerFunc: Preflight request")
  		c.handlePreflight(w, r)
  	} else {
  		c.logf("HandlerFunc: Actual request")
  		c.handleActualRequest(w, r)
  	}
  }
docs: // HandlerFunc provides Martini compatible handler