This closes #1777, fix the GetStyle or GetConditionalStyle function to returns incorrect DecimalPlaces field value

- Update documentation for the NewStyle function
- Update unit tests
- Update dependencies Go module
- Update GitHub workflow dependencies package version
- Update copyright agreement statement

Signed-off-by: Ncui fliter <imcusg@gmail.com>

- Update example code in the documentation
- Update unit tests
- Rename `PictureOptions` to `GraphicOptions`
- Adjust partial options fields data types for the `PictureOptions` and `Shape` structure
- Update dependencies module

- Add JSON tags for `AppProperties`, `PivotTableOption` and `PivotTableField` structure

- Format code with `gofmt`

- ref #65, new formula functions: DCOUNT and DCOUNTA
- support percentile symbol in condition criteria expression
- this update dependencies module

- Remove exported variable `ErrEncrypt`

Added two exported functions `SetWorkbookPrOptions` and `GetWorkbookPrOptions` to support setting and getting the code name property of the workbook
Re-order fields of the workbook properties group to improve the compatibility
Go Modules dependencies upgrade
Put workbook related operating in new `workbook.go` source code
Library introduction docs block updated

Fix file corrupted when save as in XLAM / XLSM / XLTM / XLTX extension in some case
New exported error ErrWorkbookExt has been added, and check file extension on save the workbook
Format source code with `gofumpt`

Rename exported constants `NameSpaceDublinCoreMetadataIntiative` to `NameSpaceDublinCoreMetadataInitiative`

- fix COUPPCD result accuracy issue
- update close spreadsheet example in documentation and README

- Make variable name more semantic
- Reduce cyclomatic complexities for the formula calculate function
- Support specified unzip size limit on open file options, avoid zip bombs vulnerability attack
- Typo fix for documentation and error message

- Rename exported field `File.XLSX` to `File.Pkg`
- Exported error message

Go 1.15 and later required, #65 fn: IMABS, IMCOS, IMCOSH, IMCOT, IMCSC, IMCSCH, IMEXP, IMLN and IMLOG10

lint issue fixed and new formula function: ATAN, AVERAGE, AVERAGEA, CONCAT, CONCATENATE, COUNT, COUNTBLANK, MAX