Switch data output to hdf5

[repepo]

It would be convenient to write the output data in a better way, perhaps using hdf5. Runs producing additional output should be appended to the original output files.

[AnkitBarik]

I think that can work well with hdf5, especially with h5py. However, I suggest having a switch for hdf5 output, so the user still has the choice to dump things in the current ASCII format. (np.loadtxt is conceptually much easier to understand ).