download of hourly historical solar data is invalid about wetterdienst

[gutzbenj]

Dear @e-dism ,

unfortunately I missed out on documenting this anomaly! (which you should usually find here (https://wetterdienst.readthedocs.io/en/latest/pages/behind_the_scenes.html)

I have attributed solar to the period "recent", because when looking into one of the files you will see that the data is reaching until yesterday (which is typical for the recent period as you may want to analyze on a daily basis).

I may as well add a function that lets the user print available parameters and their periods.

[e-dism]

Dear @gutzbenj,

Thank you for the fast reply. I had the thought, that you have chosen this way. I would recommend to do a "re-attribution" if the PeriodType Historical is used and add a Information to the user to inform about the change of the attribute. The current text of the exception is not very helpful to find out what went wrong.

As in #136 mentioned, documentation is very helpful to distinguish between bugs and "features" ;-)