Added an option to color out the ouput

Enhance the readability using basic colorization to the logging system.
As the '--call' option is almost unused, it doesn't require to have a
shortname. So we use the '-c' and '--color' for the new colorization
option, and keep only the longname for the 'call' option.

Change-Id: I095fc9f38133fb742e0f0003540cd120feec8f5e
Signed-off-by: Loïc Collignon <loic.collignon@iot.bzh>