python-msgpack: new package

[Thomas: convert to the Python package infrastructure, added missing
dependency on C++, inherited from msgpack.]

Signed-off-by: Wojciech M. Zabolotny <wzab01@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>