VCF文件格式信息
更多VCF格式详细信息参见http://samtools.github.io/hts-specs/VCFv4.2.pdf
##为header line,注释信息
#为data line,表头信息:
CHROM - chromosome
POS - position
ID - identifier
REF - reference base(s)
ALT - alternate base(s)
QUAL - quality
FILTER - filter status
INFO - additional information