aln文件的碱基计数器，输入aln文件及计数的起始与终止位置，输出为txt格式，统计计数范围内碱基的50列中每列包含的21个元素的数量。-aln file base counter, input aln file and count the start and end position, the output txt file within the statistical count of the 50 base 50 of each column contains the number of