also fix a typo in the vorticity equation wrapper, but the code fails
anyway, so that's not a big deal.
I still need to generate initial conditions.

Update the re-allocation of the particles array after re-distribution -- go to a simple model without memory re-use -- add a class to easily perform the same copy on position index and rhs

Remove warnings -- split the accuracy (float/double) between field and particles, use double by default for the particles

Call the spline using the position of the particle inside the cell (normalize to 0-1) -- pass an array of box width to the constructor

Add an interface builder (with runtime values for spline mode and interpolation size) -- templatize the real number types (splines still rely on double)

Update all -- dims idx are now z-y-x -- field wrapper use a memory leading array for data access -- debug rhs particles extension when re distribute the particles

In the past, if I discovered that the pp file was computed for different
iterations, I removed everything from it.
Which is a bad idea, hence I'm not deleting the datasets that I know
have to be deleted.

stupid string parameter got broken again, since I keep trying to get rid
of address sanitizer complaints.
this time, I'm just using malloc with free, and apparently all's fine.

in field io, dset_id is initialized differently depending on a couple of
things. compiler is complaining that it may be used uninitialized, so
I'm initializing it with H5I_BADID now.