说一下对 class_ro_t 的理解？
存储了当前类在编译期就已经确定的属性、方法以及遵循的协议。
struct class_ro_t {
uint32_t flags;
uint32_t instanceStart;
uint32_t instanceSize;
uint32_t reserved;
const uint8_t * ivarLayout;
const char * name;
method_list_t * baseMethodList;
protocol_list_t * baseProtocols;
const ivar_list_t * ivars;
const uint8_t * weakIvarLayout;
property_list_t *baseProperties;
};
baseMethodList，baseProtocols，ivars，baseProperties三个都是以为数组。
