Use dash instead of underscore in variable name in file name

[bouweandela]

The filenames generated by era5cli look like this:

era5_temperature_1990_hourly.nc
era5_temperature_of_snow_layer_1990_hourly.nc

The usual convention for filenames, in e.g. the CMIP5 and CMIP6 projects, is to use underscores between the different facets and dashes if a space is needed inside a facet. This makes it easier to extract the different facets from the filename. Therefore, it would be more convenient if era5cli filenames looked like

era5_temperature_1990_hourly.nc
era5_temperature-of-snow-layer_1990_hourly.nc

because then people would be able to use a glob like

ls era5_temperature_*_hourly.nc

to find just the temperature variables instead of any kind of variable that starts with temperature.

[BSchilperoort]

PR #148 implements an optional kwarg to be able to use dashes in the variable name of the file name.

The pros of the dash are:

• The filename is more readable
• It makes it easier to extract the different facets from the filename.

The cons are:

• It would represent a change in behavior of era5cli
• The CDS API uses underscored names.
  • Note that this does not align with the full names OR netCDF variable names.*
• Users input the variables they want with an underscore.
  • Would we also change this? Or just allow both as input.

* From some experimentation it seems that the cds api variables are the all-lowercase long_name, with spaces replaced by underscores.