read_stmf_files reads weekly mortality data from a file downloaded
from the Short-term Mortality Fluctuations (STMF) series available in the
Human Mortality Database (HMD) https://www.mortality.org/Data/STMF,
and constructs a vital object suitable for use in other functions.
See also
read_stmf() for downloading and reading STMF data directly from the HMD.