Pipe viewer reimplementation

pv is a Unix pipe monitoring application. (And this is copy of the much older original)

You can use it in places where a progressbar, or at least a flow rate meter, would be handy. Some handy examples:

```sh

Is it still transferring or did something freeze?

docker save excelsior | pv | ssh me@devbox.company.com "docker load" ```

```sh

Why doesn't gzip have a progressbar already?

pv gigantic-file | gunzip | gawk '/size/ { x += $4 } END {print x}' ```