* Fixed issue #539 Fixed error opening excel file created in encoding different from UTF-8, added logging of possible errors when decoding XML if the function does not provide exit with an error
* Added test for CharsetReader
* Fixed #discussion_r359397878
Discussion: https://github.com/360EntSecGroup-Skylar/excelize/pull/540#discussion_r359397878
* Fixed go fmt
* go mod tidy and removed unused imports
* The code has been refactored
workBookRelsWriter, drawingRelsWriter into relsWriter;
drawingRelsReader, workbookRelsReader, workSheetRelsReader into relsReader;
addDrawingRelationships, addSheetRelationships into addRels
* Huge refactorig for consistent col/row numbering
Started from simply changing ToALphaString()/TitleToNumber() logic and related fixes.
But have to go deeper, do fixes, after do related fixes and again and again.
Major improvements:
1. Tests made stronger again (But still be weak).
2. "Empty" returns for incorrect input replaces with panic.
3. Check for correct col/row/cell naming & addressing by default.
4. Removed huge amount of duplicated code.
5. Removed ToALphaString(), TitleToNumber() and it helpers functions at all,
and replaced with SplitCellName(), JoinCellName(), ColumnNameToNumber(), ColumnNumberToName(), CellNameToCoordinates(), CoordinatesToCellName().
6. Minor fixes for internal variable naming for code readability (ex. col, row for input params, colIdx, rowIdx for slice indexes etc).
* Formatting fixes
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