With implicit VCF indexing for VCF BED intersection

In previous version the VCF needs to be indexed with some tool like IGV tools or Tabix to run the utility.
Now the tool itself takes care of the VCF index generation with intermediate temporary index file.
One prerequisite is that the input VCF must have contig information in header in below format for all the applicable chromosomes.
##contig=<ID=chr1,length=249250621,assembly=hg19>