nicer display formats for duration UDAs

[Zocker1999NET]

When using an UDA with a duration (e.g. for the estimated time for completion), it seems that it can only be displayed in the ISO duration format. For example:

# .taskrc
uda.eta.type=duration
uda.eta.label=ETA
# (also add this to a report of your choice)

Then Taskwarrior only lists default and indicator as supported formats via task colums eta. I can set an ETA with e.g. eta:5min, but by default it gets displayed as PT15M. For dates, or rather for displaying the duration between now and a given date, Timewarrior supports other formats as well. These would highly increase the usability of duration UDAs.

So I think following format specifications could be added to durations (using the example from above):

• age for 15min, useful when exact display is not required
• countdown for 00:15:00, useful for second-precision output with hours as largest divisor
• iso for the current default PT15M

[astr0gator]

Amazing idea