Converting from other csg formats

[shimwell]

Currently CSG2CSG converts from MCNP to *

@makeclean is working on OpenMC to MCNP

In the longer term it would be great to convert from * to * and perhaps we should start structuring the code so that this is supported.

Changing the arg parsing so that an input file and format are accepted

python3 python/csg2csg.py -i ~/Desktop/serpent_docker/matti_Neutronics/DEMO_materials.serp -f serpent -o openmc mcnp

I have a short term need to create some OpenMC inputs (or at least the material cards part) from Serpent so I have created a fork

This also contains the suggested changes to arg parse