this function transforms an error log into an error message.
generateError(error.log, warning.log, line.break = "\n ")a data.frame with following fields:
sheet: character, the sheet name.
row: integer, the row position.
column: integer, the column position.
message: character, the error message.
a data.frame similar to error.log.
a character value, separation between error messages.
a character value, the corresponding error message.