Several bugs have been fixed: in the AllSky generator, the cloudiness was still forced to 0.5 (as for debug). The data creators were also called *after* the generators, thus making it impossible to used a created data in a generator. 

The placeholders have been put in place (but commented out) for the cloudiness/tau_cloud/clearness index support in MeteoData. It seems that Kt=clearness index might be the proper way to go, but this is still a messy field. Some comments have been added in the code to clarify the use of such parameters.