get_maintainer.pl: add .get_maintainer.ignore file capability

Some people prefer not to be cc'd on patches.  Add an ability to have a
file (.get_maintainer.ignore) with names and email addresses that are
excluded from being listed except when specifically listed as a maintainer
in a section.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>