Pre-1996 SIM data

[jruizcabrejos]

Currently, the package only allows downloads for data from 1996 and onwards.
However, the "SIM - Sistema de informação sobre mortalidade" has data available starting on 1979.

Data from 1979-1996 has some differences compared to data from 1996-2022
(e.g. the disease classification changes from ICD 9 to ICD 10).
Despite this, the data is still of use even if it can't be processed by process_sim yet.

It would be incredibly useful if 1979-1996 SIM data was available through the package.