signoff: enhanced mismatch support

Break up the mismatch states into "name does not match" and "email does not match", and provide a diff of the two.

Related: #197 (closed)

Samples of current output can be seen in https://gitlab.com/redhat/rhel/src/kernel/kernel-test/-/merge_requests/608#note_683483175 and https://gitlab.com/redhat/rhel/src/kernel/kernel-test/-/merge_requests/620#note_683483632

Signed-off-by: Jarod Wilson jarod@redhat.com