Overview of MESINESP, a Spanish Medical Semantic Indexing Task within BioASQ 2020 - Carlos Rodríguez Penagos; Anastasios Nentidis; Aitor Gonzalez-Agirre; Alejandro Asensio; Jordi Armengol-Estapé; Anastasia Krithara; Marta Villegas; Georgios Paliouras; Martin Krallinger (Working Notes of CLEF 2020 - Conference and Labs of the Evaluation Forum, Thessaloniki, Greece, September 22-25, 2020, 2020)