In stage 1 we will start with an Excel file hand-created on Win 10 in
a format to be a template for producing Excel files in the same format
but substituting different values in certain cells.

This test is a strict use of Excel files with Raku/Perl wrapping.

Note that no Perl module on Linux can extract the formula from an
existing Excel xlsx file so we will try a hybrid solution:

+ Design, in Excel, the template in the format we want. Insert
  place-holder text strings as values which the xlxs reader can
  extract. Those strings will be translated by the Raku wrapper and
  inserted in the output xlsx file.

+ See test template file 'hand-generated-template.xlsx' as input. That
  file converts to cvs with "ssconvert f.xlxs f.cvs" as:
