docs: def vcfunpackcall(table, *keys):
      """
      Unpack the call column. E.g.::
      
          >>> import petl as etl
          >>> # activate bio extensions
          ... import petlx.bio
          >>> table1 = (
          ...     etl
          ...     .fromvcf('fixture/sample.vcf')
          ...     .vcfmeltsamples()
          ...     .vcfunpackcall()
          ... )
          >>> table1
          +-------+-----+------+-----+-----+------+--------+------+-----------+------+------+-------+----------+
          | CHROM | POS | ID   | REF | ALT | QUAL | FILTER | INFO | SAMPLE    | DP   | GQ   | GT    | HQ       |
          +=======+=====+======+=====+=====+======+========+======+===========+======+======+=======+==========+
          | '19'  | 111 | None | 'A' | [C] |  9.6 | None   | {}   | 'NA00001' | None | None | '0|0' | [10, 10] |
          +-------+-----+------+-----+-----+------+--------+------+-----------+------+------+-------+----------+
          | '19'  | 111 | None | 'A' | [C] |  9.6 | None   | {}   | 'NA00002' | None | None | '0|0' | [10, 10] |
          +-------+-----+------+-----+-----+------+--------+------+-----------+------+------+-------+----------+
          | '19'  | 111 | None | 'A' | [C] |  9.6 | None   | {}   | 'NA00003' | None | None | '0/1' | [3, 3]   |
          +-------+-----+------+-----+-----+------+--------+------+-----------+------+------+-------+----------+
          | '19'  | 112 | None | 'A' | [G] |   10 | None   | {}   | 'NA00001' | None | None | '0|0' | [10, 10] |
          +-------+-----+------+-----+-----+------+--------+------+-----------+------+------+-------+----------+
          | '19'  | 112 | None | 'A' | [G] |   10 | None   | {}   | 'NA00002' | None | None | '0|0' | [10, 10] |
          +-------+-----+------+-----+-----+------+--------+------+-----------+------+------+-------+----------+
          ...
  
      """
  
      result = (
          etl.wrap(table)
          .convert('CALL', lambda v: v.data._asdict())
          .unpackdict('CALL', keys=keys)
      )
      return result