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).

(From OE-Core rev: 4208f1546c92f069e432d1865269ce539db8cea7)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/buildhistory-diff

@@ -53,6 +53,10 @@ def get_args_parser():
     parser.add_argument('-e', '--exclude-path',
                         action='append',
                         help="Exclude path from the output")
+    parser.add_argument('-c', '--colour',
+                        choices=('yes', 'no', 'auto'),
+                        default="auto",
+                        help="Whether to colourise (defaults to auto)")
     parser.add_argument('revisions',
                         default = ['build-minus-1', 'HEAD'],
                         nargs='*',
@@ -107,10 +111,11 @@ def main():
     elif len(args.revisions) == 2:
         fromrev, torev = args.revisions
 
-    from oe.buildhistory_analysis import process_changes
-
+    from oe.buildhistory_analysis import init_colours, process_changes
     import gitdb
 
+    init_colours({"yes": True, "no": False, "auto": sys.stdout.isatty()}[args.colour])
+
     try:
         changes = process_changes(args.buildhistory_dir, fromrev, torev,
                                   args.report_all, args.report_ver, args.sigs,