implementation of new cloudmask cm003 version, with possibility to chose cld_prb threshold (probability) and number of dilatation iterations (iterations). cm001 stays default cloudmask version

updated scihub api url changed to https://apihub.copernicus.eu/apihub/ as of 28 April 2021, more info here https://scihub.copernicus.eu/news/News00868

3 new Library functions (compute_l2a, compute_cloudmasks, compute_indices) to multi-process a list of tiles