[Kwant] Recursive Green's function method and Kwant

Hi Benjamin (and anyone else who is interested), I have made available an unfinished RGF module for Kwant in the repository http://git.kwant-project.org/experimental/kwant-rgf/. This code was written by our former student Daniel Jaschke and myself. It is not at all ready to be included into Kwant but it may be useful for you if you want to experiment with RGF in Kwant. If you come to an implementation that you like — we'd be curious to take a look. Cheers, Christoph