python-simplejson: new package

[Thomas: convert to the Python package infrastructure, drop the
setuptools dependency since the package uses distutils.]

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>