Add the "diffmanifests" command

This command allows a deeper diff between two manifest projects.
In addition to changed projects, it displays the logs of the
commits between both revisions for each project.

Change-Id: I86d30602cfbc654f8c84db2be5d8a30cb90f1398
Signed-off-by: Julien Campergue <julien.campergue@parrot.com>
3 files changed