[Feature request] Option to save stats to file e.g csv

Hi,

First of all thanks for the program 🙂

Nevertheless it'd be great if there were an option to modify the output in order to create stats and graphs once all is said and done.

A necessary option would be forcing the rates and sizes to be of a constant unit e.g bytes, KB, MB, etc.

Possible options I see would be

1. Add --newline option

Instead of simply printing ' \r' '\r\n' could be printed

Downside of this, would be that it fills up the screen.

2. Provide --csv option

Invocation could be pv --csv [OUTFILE] and depending on the display options a CSV would be generated

Time, Current in B/s, AVG in B/s
00:00:01, 65, 65
00:00:02, 73, 69

Upside of this would be keeping the normal display and not having to deal with piping the stderr.

Cheers