agenda and agendaupdate: add --details length

[michaelmhoffman]

Implements #791.

To eliminate the possibility of conflicts between length and end_date/end_time, this raises NotImplementedError if input is supplied with both of the fields.

In the future, the following would be better conflict resolution approaches:

1. allow both end fields and length field long as they are consistent in each row
2. conflict resolution by command-line option (e.g. prefer end fields or prefer length field)
3. conflict resolution interactively

[dbarnett]

Closed without merging? Did you change your mind about this change?

[michaelmhoffman]

No, I thought I was just renaming master to main in my fork, and I guess this was a side effect. Argh.

[michaelmhoffman]

Reopening

[michaelmhoffman]

I may need to make a new pull request to actually reopen. Or can just merge if you're OK with it. Or you can.

[dbarnett]

Ah funny, because michaelmhoffman:master no longer exists…

If you can open a new PR that'll probably be easiest to follow. I would try to merge the it here but the button is gone and "reopen" is disabled.