topydo may introduce some internal tags, such as 'id' and 'p' for
dependency tracking, and 'ical' for keeping track of unique ids when
outputting iCalendar files.

Add a pretty printer filter that prevents certain tags from displaying
in the 'ls' output. These tags can be configured with the 'hide_tags'
configuration option in the 'ls' section, a comma-separated list of
tags (default: id,p,ical). To always show all tags, leave an empty
value.