- refactor (breaking): rename `DataType` enum to `Data` and `DataTypeRef` to `DataRef`
- feat: introduce a `DataType` trait implemented by both `Data` and `DataRef`.
- feat: `Data` and `DataType` now return `Some(0{.0})` and `Some(1{.0})` rather than `None` when `.as_i64` or `.as_f64`
  is used on a Bool value
- fix: getting tables names on xlsx workbook without _rels files
- refactor: DateTime(f64) to DateTime(ExcelDateTime)
- feat: detect xlsb/ods password protected files
- feat: introduce is_x methods for date and time variants