wip/ics2txt v1.1 NetBSD

Convert icalendar .ics file to plain text.

Set of tools to work with the popular iCalendar format and converting to even simpler TSV and text forms.

* ics2tsv: converts the iCalendar data to an easier-to-parse TSV format. * ics2tree: lints exhaustively all iCalendar content for inspection. * tsv2ics: convert back the TSV format to iCalendar. * tsv2agenda: displays converted TSV data to readable output.

An ical.c/ical.h library walks through the icalendar structure and is used by the various ics2* parsing tools above.