Features
一个简单的全局订阅事件，回调事件的库
Getting started
Usage
/// 订阅
zqEvent.subscribe<String>('key', (param){
print('自定义触发事件回调key-1：$param');
});
zqEvent.subscribe<String>('key', (param){
print('自定义触发事件回调key-2：$param');
},index: 1);
/// 启动
zqEvent.fire('key','帅的掉渣');