Adding new functionality to publookup

I need to be able to do "gene enrichment" instead of "article enrichment". I made modifications to entrezpublookup.py to facilitate this. Now using sha: 7d6fb2540e604dd4f200e0b1014b71adb046c9f5

I re-ran the results for Peter's gene lists using the command:

python entrezlookup.py -s lists/testlist.txt -o lists/PeterResults.txt -g lists/GeneLevelOutput.txt --gene-based lists/GeneBasedOutput.txt