-cs, -ss option can cause JSON creation to fail

[zmorrell]

When using the following command:

./dwig.py -pp -cs 0,4 0,5 1,4 1,5 const -cp 0.2 -f -0.5

dwig will crash, stating "a spin pair must be x,y integers". The parser is attempting to take an arbitrary number of qubit pairs, and is unable to differentiate the "const" subparser. This can easily be worked around by swapping the order of the -pp and -cs arguments, as shown:

./dwig.py -cs 0,4 0,5 1,4 1,5 -pp const -cp 0.2 -f -0.5

The cause of this issue is in the argument parsing, and there is not an immediately obvious fix that would allow passing arbitrary coupler or spin sets.