should support both python 2.7 and python 3.6

[OriHoch]

datapackage-pipelines framework requires python 3.6, see hasadna/knesset-data-datapackage#14

currently I think best way to solve it is to have knesset-data-python support both python versions

[OriHoch]

started some work on it in #20 - but not sure if I'll have much time to continue, so if someone else wants to take - be my guest

[gilwo]

working on this issue