1.6.0 - allow NULLABLE to convert to REPEATED; add input_format=csvdictreader

• 1.6.0 (2023-04-01)
  • Allow null fields to convert to REPEATED because bq load seems
    to interpret null fields to be equivalent to an empty array [].
    See #90.
  • Add input_format='csvdictreader' option. Similar to 'dict' but
    intended to be used with the csv.DictReader class to read CSV and TSV
    files with various options. More documentation and discussions at:
    • SchemaGenerator.deduce_schema() from
      csv.DictReader,
    • Discussion#91.