Conversion function to handle multi-object files

[leeper]

If I want to update an XLS to XLSX, I have to loop over sheets. Similarly, if I want to convert an XLSX to Stata or CSV, looping is required. Because we may not know how many sheets there are a priori, this requires a while () or repeat loop, which is annoying. A solution would be a modified convert() function (or wrapper for convert()) that turns a multi-object file into another multi-object file or set of files. One could imagine this also working with multiple files in a directory as input or output.

[jsonbecker]

If this is mostly a matter of xlsx, we could use openxlsx::getSheetNames and lapply over sheets. Similarly passing a directory instead of a file could lapply over dir()