Implement logger writer
In this merge request, I am changing the API for the writer in order to be more flexible.
In the file
src/cell.c, I am also writing the particles that leaves the box and are removed from the simulation.
I propose to review it in two steps if it is a bit too large for you. We can first take a look at
logger.c and any of the scheme dependent files (e.g.
hydro/Gadget2/hydro_logger.h) and then the impact on the other files.