complete group creation endpoint with auth and validation, change parameter and return pointer usage in some get func

main.go

@@ -29,5 +29,6 @@ func main() {
 	log.Println("server listening on :8080")
 	http.HandleFunc("POST /register", RegisterHandler)
 	http.HandleFunc("POST /login", LoginHandler)
+	http.HandleFunc("POST /create/group", CreateGroupHandler)
 	log.Fatal(http.ListenAndServe(":8080", nil))
 }