ISInvocationHookProxy 挂钩目标的每个NSInvocation的代理对象

ISInvocationHookProxy挂钩目标的每个NSInvocation的代理对象。

用法：

NSString *object = [[NSString alloc] init];

ISInvocationHookProxy *proxy = [[ISInvocationHookProxy alloc] initWithTarget:object];

proxy.hookBlock = ^(NSInvocation *invocation) {

  // will be called when [(NSString *)proxy length]; is executed

};

[(NSString *)proxy length];

覆盖调用的返回值：

NSString *object = @\"foo\";

ISInvocationHookProxy