adding one basic interpolation class IpolBase from which all other classes (Nearest, Idw, Linear) inherit
adding one basic interpolation class IpolBase from which all other classes (Nearest, Idw, Linear) inherit

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