改进的SeriaPort类，实现块读取

代码说明：

基于CSerialPort类，增加了RecvBlock方法，一次性读取多个字节，并且改进了无法正常退出的bug。原说明：This class can read, write and watch one serial port.It sends messages to its owner when something happends on the portThe class creates a thread for reading and writing so the mainprogram is not blocked.