Introduce the 15-wires PLONK code

[mimoo]

This PR builds on #126 to introduce the 15-wires PLONK construction to the codebase.

In order of importance it:

1. introduces a protocol change to always leave room for the zero knowledge polynomial
2. fixes the generic gate
3. fixes the poseidon gate (closes [15-wires] fix poseidon bug #136)
4. adds a few of assertions
5. adds a number of tests
6. adds a number of (rustdoc) comments
7. refactors some places to make the code cleaner
8. merged master into this branch AND updated the code to use most recent arkworks
9. ran cargo fmt

What's the minimum that needs to be done to merge this:

• someone makes sure that the zero polynomial change is not a stupid change
• code needs to be updated to match the arkworks branch

I propose that once this is cleaner/reviewed we merge it, and then work on a) more tests to make sure all gates work, etc. and b) OCaml bindings.

[mimoo]

merged master, and added small fix to CI

[imeckler]

Yay!

[spartucus]

Hi @mimoo, are there any papers or docs about kimchi?

[mimoo]

there's https://o1-labs.github.io/mina-book/ but it's heavy work in progress

[spartucus]

Thanks :)