Publish crates to crates.io

[drskalman]

We want to publish common and ring but we need a better name for them. It was suggested that common be renamed to w3f-plonk-common. and ring should also probably rename to something like ring-proof.

[davxy]

To publish these you first need to publish fflonk I guess

But please, let's first address #36

In JAM we're also using a feature from my fork to produce test-vectors. If we switch to crates.io we need it there as well. I'll propose a PR after #36 is merged