Bugfix in Medium propagation for Air in Zone model

also adapted example to work with TMY3 reader and new example with multiple radiators in parallel.
I have updated the documentation for the zone model in ecd5f41, although I did not really find the original source.  @rubenbaetens , I got the 3.076 from IDEAS.Buildings.Components.BaseClasses.InteriorConvection, but I could not find a source.  Maybe it's not needed...