- Added property worksheet.Position to set the position of the worksheets. 
- Added overload Worksheets.Add(String sheetName, Int32 position). This way you can add a worksheet in a specific position in one shot.
- Added method range.RangeUsed()
- Added method workbook.Worksheet(String/Int32) to retrieve existing worksheets. I can't believe it never occured to me to add this before.
- Improved overall performance.
- Fixed Issue # 6807
- Reduced the size of the generated files.