code: def merge_vcfs(vcf_file, merged_mut_file):
      
      mutect_keys = set(vcf_file['mutect'].keys())
      radia_keys = set(vcf_file['radia'].keys())
      common_keys = radia_keys.intersection(mutect_keys)
      # Open as append since the header is already written
      with open(merged_mut_file, 'a') as outfile:
          for mutation in common_keys:
              print('\t'.join(vcf_file['radia'][mutation]), file=outfile)
      return None
docs: This module will accept the vcf files for mutect and radia read into memory in a dict object
      VCF_FILE and will merge the calls.  Merged calls are printed to MERGED_MUT_FILE.
  
      VCF_FILE is a dict with
      key : mutation caller (mutect or radia)
      value : dict with
              key: (chrom, pos, ref, alt)
              value: vcf line in list form (split by tab)