This question was originally asking for a custom progress indicator, but I've since removed the 'custom' requirement because I think the generalized case is more helpful to others.
I have added a command that takes a while to execute. Therefore I'd like to temporarily display a buffer with an animated textual progress indicator (rotating
\|/-, perhaps) that updates with some frequency to show that the command is still running.
What's the best way to go about doing this?