docs: def vcfmeltsamples(table, *samples):
      """
      Melt the samples columns. E.g.::
      
          >>> import petl as etl
          >>> # activate bio extensions
          ... import petlx.bio
          >>> table1 = (
          ...     etl
          ...     .fromvcf('fixture/sample.vcf')
          ...     .vcfmeltsamples()
          ... )
          >>> table1
          +-------+-----+------+-----+-----+------+--------+------+-----------+-----------------------------------------------------+
          | CHROM | POS | ID   | REF | ALT | QUAL | FILTER | INFO | SAMPLE    | CALL                                                |
          +=======+=====+======+=====+=====+======+========+======+===========+=====================================================+
          | '19'  | 111 | None | 'A' | [C] |  9.6 | None   | {}   | 'NA00001' | Call(sample=NA00001, CallData(GT=0|0, HQ=[10, 10])) |
          +-------+-----+------+-----+-----+------+--------+------+-----------+-----------------------------------------------------+
          | '19'  | 111 | None | 'A' | [C] |  9.6 | None   | {}   | 'NA00002' | Call(sample=NA00002, CallData(GT=0|0, HQ=[10, 10])) |
          +-------+-----+------+-----+-----+------+--------+------+-----------+-----------------------------------------------------+
          | '19'  | 111 | None | 'A' | [C] |  9.6 | None   | {}   | 'NA00003' | Call(sample=NA00003, CallData(GT=0/1, HQ=[3, 3]))   |
          +-------+-----+------+-----+-----+------+--------+------+-----------+-----------------------------------------------------+
          | '19'  | 112 | None | 'A' | [G] |   10 | None   | {}   | 'NA00001' | Call(sample=NA00001, CallData(GT=0|0, HQ=[10, 10])) |
          +-------+-----+------+-----+-----+------+--------+------+-----------+-----------------------------------------------------+
          | '19'  | 112 | None | 'A' | [G] |   10 | None   | {}   | 'NA00002' | Call(sample=NA00002, CallData(GT=0|0, HQ=[10, 10])) |
          +-------+-----+------+-----+-----+------+--------+------+-----------+-----------------------------------------------------+
          ...
  
      """
  
      result = etl.melt(table, key=VCF_HEADER, variables=samples,
                        variablefield='SAMPLE', valuefield='CALL')
      return result