Summary: Add "bors cancel" as alias for "bors r-"
It's just readability of the chat history.
bors cancel to cancel a PR from the queue.
|bors cancel||Equivalent to bors r-|
We already have one synonym. There's not much reason not to have two.
Custom commands? No way. It's hard enough making sure everyone understands what's going on.
- What's the cut-off? We don't want to enable every possible one.
cancelseems alright, because other parts of the app call it "canceling," but if someone proposes "stop," we might want to say no.
Since we already refer to it as "cancel"ing in other places, this makes sense, but beyond that, there hopefully won't be any more of these.
- Implemented by https://github.com/bors-ng/bors-ng/pull/1191