Working MATLAB geometry/tissue generation examples

[bjorgan]

The provided examples serve as a rough outline of how the tissue and geometry can be generated and are not working examples. This was mainly for avoiding the need to include too many files containing absorption properties. I'd rather make more coherent, runnable examples after defining a coherent library for organizing and obtaining tissue properties across both MATLAB and C (so that e.g. gpudm don't have to use this incoherent absorption_props.cpp interface, which is a strange way to do it).