Option to read XLSForm as Excel file

[matthew-white]

Add an option to import the XLSForm as an Excel file. This should be possible in Stata 13, where the existence of strLs means that there is no string truncation. (The Mata xl*() was also introduced in 13.)

[matthew-white]

We've had a couple of questions in the ODK forum that might have been prevented with this enhancement:

• https://forum.opendatakit.org/t/odkmeta-column-header-type-not-found/10617
• https://forum.opendatakit.org/t/odkmeta-input-csv-format/10618

As always, exporting to .csv is easier than it sounds. :)