Correct cells style in merge range
Fix incorrect style ID returned on getting cell style in some cases
Unit test updated and simplified code

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`

This removed 3 exported functions: `TotalCols`, `CurrentCol` and `CurrentRow`

Reduce allocation memory 20%, and 80% GC times for the row's iterator

Fixed the issue auto filter doesn't work on LibreOffice if the sheet name has spaces

- Remove second useless parameter `isCurrentSheet` of the function `SetSqrefDropList`
- Fix missing page setup of worksheet after re-saving the spreadsheet

Rename exported constants `NameSpaceDublinCoreMetadataIntiative` to `NameSpaceDublinCoreMetadataInitiative`

Unit test coverage improved

- Unzip shared string table to system temporary file when large inner XML, reduce memory usage about 70%
- Remove unnecessary exported variable `XMLHeader`, we can using `encoding/xml` package's `xml.Header` instead of it
- Using constant instead of inline text for default XML path
- Rename exported option field `WorksheetUnzipMemLimit` to `UnzipXMLSizeLimit`
- Unit test and documentation updated

ref #65, new formula function: INDEX (array formula not support yet)

Keep track of operators per function

Support check string equality with the string value of a defined name

Signed-off-by: NDokiys <dokiychang@gmail.com>

ref #65: new formula functions DURATION and MDURATION
fix incorrect example in SetSheetStyle docs

Improve unit test coverage for the functions: `NewStyle`, `SetActiveSheet`, `SearchSheet` and `deleteAndAdjustDefinedNames`
Simplify code and add comments for the function: `deleteAndAdjustDefinedNames`

Signed-off-by: NMichael Wiesenbauer <michael.wiesenbauer@ambos.io>
Co-authored-by: NMichael Wiesenbauer <michael.wiesenbauer@fau.de>

Fix call getNumFmtID with builtInNumFmt return -1