ip: Add color output option

ip: Add color output option

It is hard to quickly find what you are looking for in the output of the
ip command. Color helps.

This patch adds a '-c' flag to highlight these with individual colors:
  - interface name
  - ip address
  - mac address
  - up/down state

Signed-off-by: Mathias Nyman <m.nyman@iki.fi>
Tested-by: Yegor Yefremov <yegorslists@googlemail.com>