Update target platform to Mars M4

Change-Id: Icdfb616677bc270cc51ca1a055a448ff30a7447b
Signed-off-by: Axel Richard <axel.richard@obeo.fr>
Update developer guide

Update Defining custom identifiers & Ignoring identifiers sections.

Change-Id: If1fe32f84a407a7ea2bdde8a83b3cc2dc43f808d
Signed-off-by: Axel Richard <axel.richard@obeo.fr>