Batch verification

[burdges]

We should support batch verification. I wrote up some pseudo-code here:

https://gist.github.com/burdges/079d24dba55e5033117d8a3b7f26ca4f

We could clear up that code, make it into a micro crate here, and use that microcrate in the verifier, so you pass the PlonkishAcc or whatever we call it, into the verifier, and the verifier uses it for its two MSMs and and pairing.

We could generalize this somewhat of course, but it seemed to specilize the code to the plonk-like setting: two small fixed size msms on g1, double miller loop, and fixed g2 elements. We could specilize this further by adding another MSM for the DLEQ proofs.