Read the minimally allowed temperature from the parameter file and convert it to a minimal internal energy per unit mass.

The lenghts are checked against the expected values and cause an error, the labels are not currently used (would need to add API to return the headers so that these could be speculatively queried and the stream rolled back, so maybe not a great idea).

When compiling with the iosthermal equation of state, read the constant thermal energy from the YAML file.

Updated the way we converge towards the smoothing length. We now use a Newton-Raphson scheme. This applies to the Gadget-2 scheme.

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).

Added a maximal smoothing length that can be used to prevent particles from becoming too big in vacuum cases near the box edges. Will break the accuracy of the hydrodynamic scheme but is necessary in some situations.