[ENH] read z_bamf in addition to z_st; change coordinate 'layer' to 'level' for clarity
I propose to leave the concept of homogeneous layers completely internal to SCIATRAN. BAMFs and weighting functions are output by SCIATRAN on a grid. The grid of the BAMFs and weighting functions is in principle z_bamf, which can be picked up from block_amf.dat.