WIP: Data validation support

[jmcnamara]

I have started to work on the data validation feature. If you are interested in updates or trying it out add a comment/+1 here.

Equivalent XlsxWriter feature: https://xlsxwriter.readthedocs.io/working_with_data_validation.html

[jmcnamara]

I've added support for Excel data validations to rust_xlsxwriter v0.70.0.

Data validation is a feature of Excel that allows you to restrict the data that a user enters in a cell and to display associated help and warning messages. It also allows you to restrict input to values in a dropdown list.

Here is an example:

use rust_xlsxwriter::{DataValidation, DataValidationRule, Workbook, XlsxError};

fn main() -> Result<(), XlsxError> {
    // Create a new Excel file object.
    let mut workbook = Workbook::new();
    let worksheet = workbook.add_worksheet();

    worksheet.write(1, 0, "Enter rating in cell D2:")?;

    let data_validation = DataValidation::new()
        .allow_whole_number(DataValidationRule::Between(1, 5))
        .set_input_title("Enter a star rating!")?
        .set_input_message("Enter rating 1-5.\nWhole numbers only.")?
        .set_error_title("Value outside allowed range")?
        .set_error_message("The input value must be an integer in the range 1-5.")?;

    worksheet.add_data_validation(1, 3, 1, 3, &data_validation)?;

    // Save the file.
    workbook.save("data_validation.xlsx")?;

    Ok(())
}

Output:

See DataValidation for details.