settings tip: show an expansion level in front of expanded columns

[midichef]

A tip for those working with nested data, like JSON: you can make expand-cols prefix the column name with a character, for every level it expands. Just change a couple of settings in .visidatarc.:

vd.option('fmt_expand_dict', '›%s.%s', 'format str to use for names of columns expanded from dict (colname, key)')  #default is '%s.%s'
vd.option('fmt_expand_list', '›%s[%s]', 'format str to use for names of columns expanded from list (colname, index)')

As a column is expanded, its name changes: element -> ›element.children -> ››element.children[0]. The change in prefix makes it faster to see which columns are expanded. Try it out!