Settings display updates:

- Now checks for no options and return blank (radio, multi-check,
select).
- Description ('desc') argument now rendered underneath input control if
not empty  (radio, multi-check, select).
- All output saves to $html variable first before echo call for
consistency (radio, multi-check).
- Select now uses 'label_for' argument correctly (like text and
textarea).
Added line breaks in HTML source output for readability.