Handle .vy files

[maurelian]

I think using a locally install vyper is probably the ideal for now. I also think that using
-f combined_json has a similar output to solc so it should be easy enough to integrate?

When in doubt, ask your friendly vyper devs: https://gitter.im/ethereum/vyper

[dmuhs]

Reopening. I'm still on this as soon as time allows 👍