checkpatch: colorize output to terminal

Add optional colors to make seeing message types a bit easier.

Add --color command line switch, default:on

Error is RED, warning is YELLOW, check is GREEN.  The message type, if
shown, is BLUE.

Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Petr Mladek <pmladek@suse.cz>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>