Add a data transfer/download-specific progress meter

[IanButterworth]

It would be nice to be able to do something like

using Downloads, ProgressMeter
p = ProgressData("Downloading x")
Downloads.download("url", progress = (total, current) -> update!(p, total, current))

(Downloads.download already has a hook for a progress callback with those args)

and get

Downloading x: 53%[=====================>                    ]  2.2 GiB of 4.3 GiB @ 1.2 MiB/s. ETA 12:32:31

[IanButterworth]

juliaup has a nice one, assuming it's from rust

[tecosaur]

This is something I've just added to one of my own packages:

One of the important things in the implementation is having a moving average for calculating the ETA (I use the last 30s of data).