Clarify what happened to Spanish subdivisions

In the past 4 months there has been a shift in how Spanish subdivisions are handled.

The [ISO list](https://en.wikipedia.org/wiki/ISO_3166-2:ES) is mixed language-wise, provinces are named in their majority language, hence Lleida instead of Llerida, etc. This was the approach taken by the dataset as well. In 2018 the ES list changed:
1) The province list has been separated into es/ca/ga versions. This makes sense at a glance.
2) The provinces were rekeyed, the previous keys were province names, now we're using the codes (C/VI/AB/etc). This is confusing, cause the key is supposed to be used when formatting an address, but Spain doesn't use codes that way, they always write the province names.
3) The ISO codes have been removed (no isoid for any of them). This looks accidental. Other countries have ISO codes defined even if the subdivision is keyed by the short version of the code.

So, I'm asking for clarification, and treating #3 as a bug.

I've had to revert to the 2017 version of the list in commerceguys/addressing, cause even the translation change was confusing users, who were used to the mixed list.