Comment 2 for bug 231189

Okay, this is in progress. A very basic version is working in the branch linked to this bug.

I may need some extra data on what people expect to see in their calendar programs, since the data TKDO tracks isn't really the same as what iCalendar expects. For example, TKDO tasks have a due date, but a VEVENT needs both a start and end date. TKDO has task files and projects, and I'm not yet sure what type of categorization iCalendar has.