aawsome

I rebased this PR. Now that 1.0.0 is out, is there anything I can do to get this PR merged?

Added some tests. Almost all new code is covered by these tests. The exception is `AddCommandGroup` when `helpCommand` is manually set. (In this case most people would anyway directly specify...

Is there anything I can do to help getting this PR merged?

> @aawsome Branch has conflicts. Could you rebase? So that if it's ready by the time @jharshman has a another look? is rebased.

From my side, I'm fine with getting this merged. Actually realized that this PR is now waiting now for more than two years - that's quite some time... Anyhow, if...

I rebased and fixed the test that was failing bacause of the automatically-added `completion` command. This PR should be now ready for merging.

Sorry if this sounds rude. This PR is now open for 2 1/2 years. I always almost immediately answered to any question or request. Which was in last history mostly...

rebased after #3148 was merged.

@MichaelEischer I included your proposals and also rebased as #3139 is merged now. The `prunePlan` struct was quite handy ;-) > `restic prune --json` still prints a lot of non-JSON...

rebased.