Merge rows and sheets of all excel files

1. Place all the "xls" type files in the same directory to "excel_merger.py"
   

2. Run the script with Python 3.11 or above
   

3. The script merges all sheets across the files and merged output is saved in the file "merged_file.xls"
   Original files are not changed in the process.

4. Rows on all sheets are sorted by first column value
   

5. Duplicate rows are removed in all sheets