Better function name for the first initialiation of all the parts at the very start of engine_init_particles()

Add the possibility to read basic chemistry information from the parameter file and propagate this onto the particle at initialisation time. More uniform naming convention for the first initialisation of properties.

Better naming convention for the cell_split variables in the YAML file. New variable for the splitting of gravity pairs.

Separate the time-step information for hydro and gravity tasks into two different set of variables for each cell.

Use the threadpool to collect data over the top-level cells at the end of the timestep. Also only loop over the cells that have tasks in their hierarchy.

Instead of listing local cells only, list cells that have a tasks associated with them on the local node.

Lots of refactoring to tidyup code reuse

Keeps the memory use down

add a parameter for space_subsize_self_grav, gravity self-interactions on cells with more than this number of particles will be split up.

Updated the default values of space_subsize_pair space_subsize_self to the optimal values found in a parameter search using EAGLE_25 on 16 cosma-5 cores.

Removed the now unused space_maxcount global variable. Documented the new YAML parameters in the example parameter file.

Replaced global variables by a new hydro_space struct that is part of space. This struct is then passed on to hydro_init_part, and used to initialize the Voronoi cells. For non SHADOWFAX_SPH schemes, this struct is empty. Replaced random_uniform declarations in some unit tests with the tools.h version. Added some more comments to 3D Voronoi code; it is now almost completely documented (meaning I almost completely understand it now).

Compute the total mass in the system and add a variable to the gpart to record how much mass they interacted with via self-gravity.

Added the option to replicate the particles along the axis to create artificially larger test cases. Driven by the parameter 'InitialConditions:replicate'.

one big messy commit for the status quo, forces sorts of the active cells in each step, does not use task_type_sub_*, and probably sorts some cells twice. but it works.