buildhistory-diff: add support for colourising the output
Colour value removes in red and additions in green, making it easier to scan the
output for relevant changes.
This adds a --colour option to specify whether colouring should be on, off, or
detected. The default is detected, and depends on whether stdout is a TTY (same
behaviour as git).
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
