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.

Wrote first working version of 1D moving mesh code. Got stuck in mesh steering and correct slope limiting.