Progress events #10
Description
It'd be nice if this lib could emit progress events during conversion. That'd be helpful to e.g. show a progress bar on ZoomHub. (As well as e.g. for user feedback in a CLI.)
Adding this to the IM implementation should be easy, but VIPS is harder, as it abstracts the whole thing away and doesn't emit progress events either AFAIK.
One idea @gasi and I discussed was to watch the output level directories for generated tiles. Don't know how feasible that is though, e.g. across platforms, Node versions, performance, etc.
If that proves to be a non-starter, another approach is to just fudge it with a timer. E.g. every second, see how many tiles have been generated, and emit the event then.
This isn't high-priority; just capturing these ideas.