Release candidate 2 for v4.0

This is a release candidate rc2 towards v4.0, it solves the following issues:
#69 #70 #71 #72 #73 #75

as a side note, the previous rc1 solves issues #50 #57 #59 #60, #61, #63 #64 #65 #66 #67
in summary all issues with the black tag (implem dev)