This function converts the excel files into required RData format.
excel2rdata(file.align = 'alignment.xlsx', null.tokens = TRUE, len = len)
the excel file name which we want to convert it into required RData format.
logical. If TRUE, 'null' is added at the first of each source sentence of the test set.
the number of sheets of the excel file to be converted into RData format. It must be assigned by the user.
an RData object as 'file.align.RData'.