save current list of valid subgraphs with scores etc. if Queue is empty or something crashed
Merge pull request #18 from waltherg/save-intermediate-results

save current list of valid subgraphs with scores etc. if Queue is empty ...
save all fragments that contribute non-zero summand to coefficient of characteristic polynomial
Merge pull request #19 from waltherg/save-all-nonzero-terms

save all fragments that contribute non-zero summand to coefficient of ch...
don't reimport time module