* Update silence add/update flags
- Change --expires/-e to --duration/-d
- Change --expires-on to --end
- Add --start
* update subcommand returns ID of new silence
The silences printed before were accurate, except
they had the old ID. Now the new ID is returned.
* Duration is added to silence.StartsAt
When a user supplies a duration to update a
silence, it is applied to silence.StartsAt after
any potential changes to the silence's start time.
19715022a4