MySAC 0.4b 发布

MySAC (MySQL Simple Asynchronous Driver) 是一个C语言的类库，用来提供异步的 MySQL 数据库服务器连接和命令发送。它使用官方的 MySQL 客户端开发包作为认证和网络连接功能。可以在代码中进行内存的管理。

新版本改进内容：

1. 增加了 Statement 的实现；
2. 增加了新的io函数；
3. This function can be always called in place of context functions: mysac_send_database, mysac_send_database, mysac_send_query,... and mysac_connect.
4. A bug in which columns were counted in place of rows was fixed.
5. A wrong file descriptor in an example was fixed.
6. A function that cannot return status was fixed.
7. A compilation error was fixed.
8. The exemple directory was cleaned from a makefile error