Add commit in an attempt to force refresh of gh-pages
Add options to select grouping criteria
Nest 'CSV Data' within section for 'Authors'
Add markup for stats and CSV export of selected categories
Simplify values of options for categories

I now expect to prepare a precomputed index for each category
in a separate property named after the radio button value.
Add suffix '_categories' to each radio button value for disambiguation
Rename 'data-output' element to 'selected-authors-csv-output'

The change differentiates this element from the element for the export
of CSV data of selected categories.
Add text inputs for all principle variables in filters section