Added code to translate "HTML" markup inside an existing spreadsheet.

Updated phpspreadsheet version.

Updated unit tests.

Patch to setNumericCell if an empty string is passed in as value.

Updated to demonstrate sheets with advanced arguments undeclared

Changed 'Spreadsheet' to 'Workbook'

Updated test 'multiSheetCreatesFileWithMultipleSheets' to mimic readm…

…e example

Created excelDateToCarbon.

Updated composer to allow for lower versions of Illuminate.

Added documentation.

New method so Tony can process Uploaded files without copying them to…

… a temp directory.