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).

3D SHADOWFAX_SPH compiles again (but does not really work). Re-introduced global variables to store the box size.

Re-added version of dopair1_vec that does not process 2 pi at the same time and use 2 vectors for interaction loop.

Added more in depth timers for interaction functions and added macros to choose which versioin of DOSELF1 to use.

Only one argument now

Move rho_dh into the density sub-structure. Update the pressure and sound-speed after kick and drift