Add coreasshower class

This is a big refactoring of the numpy.io code, introducing a new class (CoreasShower) which can be used to read in a CoreasHDF5 into a Shower like object. This is useful in comparisons, as it allows one to more easily interact with the antennas in the Coreas simulation and transfrom to other CS, as the Shower class has a method to calculate the cstrafo.

It also includes updates and fixes to the (Numpy) documentation.

Since this is a quite a big change, I have bumped up the version number to 0.6, marking a big step forward for our development!