MIN: add `get_attr` and `get_attrs` to `RadarVolume` for easy access to groups
MIN: add `get_attr` and `get_attrs` to `RadarVolume` for easy access to groups

kmuehlbauer/wradlib,wradlib/wradlib,heistermann/wradlib,heistermann/wradlib,kmuehlbauer/wradlib,wradlib/wradlib