不受计算机字长限制的大整数类BigInt, 能在BigInt之间、 BigInt与int之间能进行+、-、*、/、 等运算，能进行比较，能数字与字符转换。-Computer word length limit is not a big integer class BigInt, between in BigInt, BigInt and int can be+,-,*,/, among other operations, can be compared to numbers and chara