add country/pollutant CLI options to airbase all

[avaldebe]

At work we need to download all observations/sites for 6 different pollutants.
At the moment we invoke the CLI 6 times as follows:

airbase pollutant SO2
airbase pollutant PM10
airbase pollutant O3
airbase pollutant NO2
airbase pollutant CO
airbase pollutant NO
airbase pollutant PM2.5

after merging this PR we'll be able to write

airbase all -p SO2 -p PM10 -p O3 -p NO2 -p CO -p NO -p PM2.5

It will also be possible to restrict the download to specific countries on the same CLI sub-command, e.g. downloading the same pollutants only for Norwegian, Danish and Finish sites

airbase all -p SO2 -p PM10 -p O3 -p NO2 -p CO -p NO -p PM2.5 -c NO -c DK -c FI

It might be possible to consolidate the other sub-commands (after a deprecation cycle), as their functionality is provided here.

[JohnPaton]

Ah nice, so the arguments act like filters on all? That makes sense to me from a user perspective. This is probably faster with the parallelisation as well.

[avaldebe]

Ah nice, so the arguments act like filters on all?

Yes, it restricts/focuses the download to only a few pollutant/countries

That makes sense to me from a user perspective. This is probably faster with the parallelisation as well.

It should be faster to request multiple pollutant/countries at once than requesting them one by one, but I would guess that the difference is small.

This is mostly an UI/UX update based on the feedback from my colleague putting the CLI in production.

What do you think about consolidating the CLI sub-commands?
airbase pollutant NO2 --country NO and airbase country NO --pollutant NO2 are
equivalent to airbase all --pollutant NO2 --country NO, so we could remove the sub-commands altogether and write airbase --pollutant NO2 --country NO (implicit all sub-command)
I can write deprecating workings for airbase pollutant and airbase country
and remove them from v1.0 on a separate PR

[JohnPaton]

Yes I think this sounds like a good idea. Let's indeed deprecate them for now and add the new API already, and then we can remove in 1.0

[avaldebe]

I added added a new CLI sub-command airbase download, with the same options and functionality of airbase all. Now airbase all, airbase country and airbase pollutant write a deprecation message before starting the download.

I would like to add a short entry to the README and the docs about airbase download, and maybe some tests before asking for a review.

[avaldebe]

I added the CLI to the README. The docs need some updating after merging #41

[JohnPaton]

This looks nice, thanks for updating the readme as well! Just a few quick questions but I think this looks pretty much good to go.

[JohnPaton]

Thanks, as always!