Add prettyping, a wrapper to colorize and simplify ping's output.

`prettyping` runs the standard `ping` in the background and parses its
output, showing the ping responses in a *graphical* way at the terminal
(by using colors and Unicode characters).

`prettyping` is written in `bash` and `awk`, and is reported to work on
many different systems and different versions of `awk`.

(schmonz)