Read KNMI files locally about hydropandas

[OnnoEbbens]

Yeah good idea! The functions get_knmi_daily_rainfall_url and get_knmi_daily_meteo_url need to be modified slightly to allow this.

[OnnoEbbens]

some extra wishes:

• read all parameters from a knmi file as an ObsCollection
• add normalize_index to all timeseries
• make parameters more consistent. start, tmin, startdate are all interchangeable

[OnnoEbbens]

Another wish: merge the from_knmi, from_nearest_xy, from_obs and from_knmi_file to one single method. Move all the logic to the io_knmi module

[martinvonk]

Another wish: merge the from_knmi, from_nearest_xy, from_obs and from_knmi_file to one single method. Move all the logic to the io_knmi module

We could also rename from_knmi to from_station and let from_knmi autodetect whether the first argument is a tuple with x and y (call from_nearest_xy), is an int (call from_station), is a str (call from_kni_file) etc. Then we can also leave the other methods intact at this place?