第二个接口：创建事项

[shaunthegeek]

https://help.coding.net/openapi#6656f7e04229a4da4db4967ecb1b16b8

[shaunthegeek]

复制第一个接口的代码，发现有重复的地方，比如 构造、抛异常 和 setToken，打算做一个基类继承

https://github.com/Coding/coding-sdk-php/blob/8a1aaa8546101f63bc833fe6c944d2810fc3c7b9/src/Iteration.php#L35