Sph properties

Once !159 has been merged in, this merge request improves the handling of SPH parameters by actually reading them from the YAML file and not simply using the constants from const.h

See merge request !160

Timed outputs

Fix to #161.

Also corrects the run script for the external point mass that used to regenerate the ICs every time. 

See merge request !163

Timed outputs

This implements the improvement #142.

The time of the first output and the time difference between subsequent outputs can be specified in the parameter file. So no dumps after a fix number of steps any more.

Users can also specify a unit system for the snapshots. That gets passed along to the routines dumping the snapshot. 

I have updated all the YAML run scripts as well.

See merge request !159

Fix parameter file parsing for duplicate names

The parameter file parser now checks for duplicate parameter names within sections and standalone parameters. It also checks for duplicate section names.

See merge request !161

Removed an extra kernel_igamma from the rho_dh calculation

There was an extra kernel_igamma in the calculation of rho_sh which was causing an offset to equivalent Gadget-2 runs. 

See merge request !162

Added check for duplicate parameters, both within a section and standalone and check for duplicate sections.

Exchange all foreign particles

Should fix #93.

See merge request !158

Commented out, note gparts test is unchecked.

When moving foreign particles to the end of the list, make sure we don't swap with one that is a foreign particle.

Proper name for entropy variable in Gadget-2 output

Fix to #151. 

See merge request !157

Time the initialisation step as well.

In times of difficult debugging that's the most minor change ever. The 0th time-step now also has an output displaying the wallclock time spent.

See merge request !156

Faster compilation

In the current master, every time we edit a file, we re-generate version.h which then triggers recompilation of a lot of file that include it. 

Here we re-generate a version_string.h instead that is only included in version.c. That speeds up the compilation when only a few files are modified.

See merge request !155