Log interpolation
This MR adds the option to use log interpolation within radixmath/interpolation. It also updates the radixmath python bindings and radixio/examples/radixsnd2arl to use the new method.
This change breaks compatibility with previous versions as a new parameter has been added to the two interpolation methods; however as it is not widely used yet (only by radixsnd2arl and NFDB, which will also be updated) this should not be a problem.