Minor updates to make the "read"-class version independent

[Kajwan]

Simplified parts of the code and edited some documentation.
It should now run for both the original version and new version of FABIO, as well as the calorie version.
I am a bit unsure about the versioning, but I use "1.1" for the original version (years 1986-2013) and "1.2" for the new version (years 1986-2020). It also works for the calorie version of FABIO.

There is still room for improvement. It should be made independent of io_codes.csv and su_codes.csv files and instead produce that information based on items.csv, regions.csv, and information stored in the RDS files. In that way it will become more robust.

[martinbruckner]

There are some conflicts. Please, those contributing to the python-import app try to resolve them. Thanks!