Some various cleanups
Increase the amount of sub-sampling
Cosmetic changes
Sum each file independently, then sum the resulting arrays. Should help a little with fp addition errors
Implement an option to get the gas density, rather than HI
Switch to interpolating the mass rather than the density.
The density was appropriate when we were using cloud-in-cell,
but for SPH it isn't really, because of low-density particles that
can stretch across many many cells that it will get wrong.
Implement adding particles to the grid using Kahan summation, to
minimise floating point error.
Add particles to the grid that are within 1 smoothing length of the grid, and so have some contribution to it
Adjust checking now the particles go over the outside of the grid
Remove the TotalHaloHI plots as they have no purpose now - everything can be done with HaloHI
Some pylint changes