Displays the overall time & percentage in a single self-updating line while copying with `cpv`.
Until now, `cpv` has shown that for individual files only instead of the whole operation, when copying recursively. See http://unix.stackexchange.com/a/65222 for details.
E.g.:
```
> cpv phone /media/user/Backup/phone
[...]
phone/DCIM/Camera/IMG_20150410_124506.dng
16.37M 100% 14.88MB/s 0:00:01 (xfr#6035, ir-chk=2539/8915)
phone/DCIM/Camera/IMG_20150410_124506.jpg
1.66M 100% 4.77MB/s 0:00:00 (xfr#6036, ir-chk=2538/8915)
phone/DCIM/Camera/IMG_20150410_124528.dng
16.37M 100% 16.93MB/s 0:00:00 (xfr#6037, ir-chk=2537/8915)
phone/DCIM/Camera/IMG_20150410_124528.jpg
1.68M 100% 1.40MB/s 0:00:01 (xfr#6038, ir-chk=2536/8915)
phone/DCIM/Camera/IMG_20150411_115839.dng
16.37M 100% 31.31MB/s 0:00:00 (xfr#6039, ir-chk=2535/8915)
[... scrolling and scrolling ...]
```
vs. in simply one line updating itself:
```
> cpv phone /media/user/Backup/phone
10.89G 26% 27.12MB/s 0:06:51 (xfr#8042, ir-chk=2174/10561)^C
```
* cp plugin: change cpv to function so that completion works
* cp plugin: show numbers in units of 1024 (K,M,G,T)
Use `-h` level (3): output numbers in units of 1024.
See the manpage of rsync for more information.
* cp plugin: add a README file
* cp plugin: recurse directories
* cp plugin: remove `--` to separate files from options
This has some undesired effects, like having `cpv --help` be a file
not found error.
Use `--` yourself if you need it (which you generally don't):
```zsh
cpv -- -some-file-with-hyphens.txt /tmp
```
Added this same info to the README.
