Add message bindings
Add message bindings

Add C++ bindings for the sd_bus_message_* class functions.  This
binding creates a unique_ptr wrapper around sd_bus_message*, using
the appropriate sd_bus_message deref calls when the unique_ptr leaves
scope.

Change-Id: Ieb8b981a43406332ed3b65bc5326a0f18671d496
Signed-off-by: Patrick Williams <cbb7353e6d953ef360baf960c122346276c6e320@stwcx.xyz>

openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus