[Feature] Extend ind_from_latlon with station altitude option

[leuty]

The COSMO/ICON consortium standardized how the "closest grid point" is defined when a station altitude is specified as well. They found that it is important to give substantial weigh to the altitude. I.e., it is better to use a grid point from the next valley that has the same altitude than one from the same valley with a very different ASL:

200810_pka_GP-allocation_COSMO-Newsletter.pdf

depends on Pull Request #59