Added color coding to output

[JiaT75]

[ecki]

You might want to review those requests closely, the author is involved with the xz backdoor.

[ZLima12]

I only quickly skimmed over the changes here, but "adding color coding" is not all that is happening here. seatest_header_printer is also modified to accept the length of s as a parameter, rather than computing it manually in the function. This puts the responsibility on the caller to provide the right length. I don't see why this would be necessary, instead of just letting the function use strlen as it was.