MHD simulations

Miguel has asked for the latest in MHD simulation cubes. so, i have read data with Python, instead of C++. it is a lot faster to write the code and test it. it is also to process and update.

1. Read the density array: split the lines in parts
2. Store the data in density_data[] and reshape it.
3. plot select slices along z, and they are okay.
4. Now read density and velocities.