Conflicts:
	examples/main.c
	src/const.h
	src/engine.c
	src/engine.h
	src/space.c
	src/units.c
	src/units.h

Conflicts:
	src/Makefile.am
	src/runner.c
	src/task.c
	src/task.h

size_t

Another batch of `size_t` fixes, i.e. replacing `int` counters over the particles by `size_t` to allow for more than 2G particles per rank.

There's no hurry for this, mainly cosmetics and future-proofing.

See merge request !137

First version of main() using a parameter file to get constants.

That's pretty big but does not touch the physics, the parallelisation nor MPI.

In brief:
 - Latest version of the parser from @jwillis 
 - More uniform name of functions in the unit module.
 - Added the ability for the `engine`, `space`, `unit` and `partition` objects to construct themselves from a parsed parameter file.
 - Added an example yaml file with full documentation.
 - Added yaml files and run scripts for the Sedov, Sod and uniform examples. 
 - General tidying of the `main()`.
 - Dropped the dependency on z-lib which we don't use.
 - Updated the README to reflect the new command-line parameters.
 - Cleaned-up the `main()` such that the only command-line parameters read in are policies and debugging options. 
 - Added the option to do a 'dry run'. This reads the parameter file, allocates the memory required by the ICs but does not read anything and constructs a space and engine. This allows us to check the validity of a given parameter file.

Happy to guide you through the changes if need be. 

This closes #81.

See merge request !140

Updated the run scripts to generate the ICs if they are not present. Removed the outdated global 'run.sh' script.

Updated difffloat

Two changes:

 - By default, `testPair` does not produce cells with perturbed positions.
 - The difffloat script takes an additional (optional) argument to specify how many lines/particles have to be checked. I have updated the bash scripts to follow that new policy.

Re-assign to me if you are happy with it. Thanks !

See merge request !142

Conflict with gparts changes

Conflicts:
        src/runner.c

Corrected sod shock ICs

This fixes issue #135. I had forgotten to push the updated version of the Sod shock IC script when updating the smoothing length definitions last week.

I have also added the definition of the unit system used in the run to the ICs. These are currently not used but we are working on converting ICs to internal unit system with Tom. 

See merge request !139

fix genuine problem detected by cppcheck.



See merge request !141

Added a command-line option '-d' to execute a dry run which read the parameter file and opens the ICs to check whether everything is OK.