flattabler 1.2.0

Change the implementation of [read_excel_sheet()], [read_excel_file()] and [read_excel_folder()] functions to use the readxl package.
Parameter [allSheets] to obtain all the sheets of all the Excel files in a folder: [read_excel_folder()].

flattabler 1.1.0

Functions to work directly with Excel files: [read_excel_sheet()], [read_excel_file()] and [read_excel_folder()].