function used to parse the XML file used to store the characteristics of MODIS Land Products and store them in the "prod_opts" data frame
MODIStsp_read_xml(prodopts_file, xml_file)NULL - retrieved data are stored in the specified RData file
string filename of the RData in which to store the data parsed from the XML file
string filename of the XML file containing the MODIS products characteristics
Lorenzo Busetto, phD (2014-2017)
Luigi Ranghetti, phD (2015)
The function parses the XML file product by product, stores data in a data frame and saves the data frame within the "MODIStsp_previous" RData file as a list of lists