Added ZoomScale SheetViewOption

Add iterator method for rows

- godoc and go test has been updated

- go test and godoc has been updated

Accessible value between 10 - 400

Used as:
xlsx.SetSheetViewOptions(sheet, 0, excelize.ZoomScale(75))

Accessible value between 10 - 400

Used as:
xlsx.SetSheetViewOptions(sheet, 0, excelize.ZoomScale(75))

- go test and godoc has been updated

- Fix `checkCellInArea()` index out of range when merged cell ref is single coordinate, relate issue #206;
- go test updated;
- Repository icon for SourceTree has been added

- go test and godoc has been updated

- Add categories or values on reverse order (orientation of the chart) support, and set auto or fixed maximum, minimum of the axis, relate issue #202;
- go test and godoc has been updated

- Update the function `NewSheet()` to handle when already exists a worksheet of the same name, relate pull request #196;
- go test and godoc has been updated

- New function `SetSheetRow()` has been added for support write whole line at once, relate issue #96 and #194;
- go test and godoc updated;
- Note that this function performance has not been tested

- godoc and go test has been updated

- Update the function `AddChart()`: clustered, stacked and 100% stacked bar and column series charts supported, relate issue #190;
- go test and godoc has been updated

- go test and document has been updated.

- Fix ineffectual assignments in Go code;
- Godoc has been updated

Speedup `SetCellStyle()` more.

The recent improvement to SetCellStyle still loops
over all the rows before the area, moving the area checks
into the loop is more concise and faster.

Since the loop now covers the correct area by construction,
the inner loop check checkCellInArea is no longer needed.

This reverts commit e4611e9e.

xlsx.SetCellValue() now supports bool value

make SetCellStyle quicker by skipping conversions in checkCellInArea,…

make SetCellStyle quicker by skipping conversions in checkCellInArea, and skipping area checks when we are sure the cell can't be before or past the current row/col
Signed-off-by: Matthieu Bresson

- go test updated

- go test updated