Add a example skeleton plugin

Change-Id: I16c4e9c90395648dc3d583687c97f4b72401be8b
Signed-off-by: Kevin Rocard <kevinx.rocard@intel.com>
Merge pull request #3 from 01org/skeleton_plugin

Add an example skeleton plugin
Merge branch 'master' of https://github.com/01org/parameter-framework