It assumes that the columns names have not been altered and are:
c('VariableName', 'Description (optional)', 'Type', 'Minimum', 'Maximum', 'Levels')
To override these column names specify colnames as an argument, ensuring
that the content of the columns is in the above order.
As of the time of writing, the origin date in Excel is 30 December 1899.
To override this specify origin="yyy-mm-dd"
To read in only part of the excel sheet specify the desired range (ie range="A1:F6")