Creates a 100% 'pure local' paperwallet from a local image using PIL
From commandline: (paperwallet.py pubKey privKey image fontSize font)
python python-paperwallet/paperwallet.py MyBtcOrWhateverPublicAddress MySuperSecretPrivateThatKnowOneKnowsButMeKey /path/to/paperwallet.png 13 path/to/font.ttf