second attempt to add the VCF exporter

The VCF exporter finally generates output that can be used in R.
Could you do this instead and remove the need for the textwrap library:

```python
vcf_file_header = """##fileformat=VCFv4.1
##fileDate={0}   
##source={1} 
##reference=GRCh37
##FORMAT=<ID=GT,Number=1,Type=String,Description="Genotype">
##FORMAT=<ID=AD,Number=.,Type=Integer,Description="Allelic depths for the ref and alt alleles in the order listed">
##FORMAT=<ID=DP,Number=1,Type=Integer,Description="Approximate read depth (reads with MQ=255 or with bad mates are filtered)">
##FORMAT=<ID=GQ,Number=1,Type=Float,Description="Genotype Quality">
#CHROM\tPOS\tID\tREF\tALT\tQUAL\tFILTER\tINFO\tFORMAT
""".format(time.strftime('%Y%m%d'), vcf_source)
```