Output the position of the cell in the output of the periodic boundary condition test. Better tolerance requirements.

Corrected mistake in the periodic boundary test that prevented compilation when optimisations are switched off.

Make the difffloat script use a new line in the files to set a limit below which values are ignored as too close to zero.

Moved the testing into a function and tested each corner cell and each cell at the centre of each face.

Created a branching function for DOPAIR1, so that the scalar version is called if it is a corner interaction when the code is vectorised. Also fixed a bug with runner_dopair1_density_vec so that hi_max and hj_max are used to find how many particles to read into the cache.

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.