利用VHDL语言完成LED显示基本功能，并且补充了一些特殊功能-LED display using VHDL language to complete basic functions, and added some special features

十进制计数器（异步置数）及七段数码管显示系统，VHDL语言-Decimal Counter (Asynchronous Set the number) and the seven-segment LED display system, VHDL language