Memory leak in input graphs

[CSpaccasassi]

The memory print of genCRN grows larger when a very large number of input digraphs are passed to as input. We observed that when passing all possible input digraphs for 2 species CRNs (around 12 million digraphs) to a single instance of genCRN, the memory footprints grows to around 100 MB. This issue has not been a problem for the cases we have analysed, genCRN generally had a memory footprint of around 2MB.